diff --git a/crates/middleware/Cargo.toml b/crates/middleware/Cargo.toml
index 898de7e2fa8..914a30389e4 100644
--- a/crates/middleware/Cargo.toml
+++ b/crates/middleware/Cargo.toml
@@ -14,4 +14,6 @@ exclude.workspace = true
 [dependencies]
 alloy-json-rpc.workspace = true
 alloy-networks.workspace = true
+alloy-primitives.workspace = true
 alloy-transports.workspace = true
+futures-util = "0.3.28"
diff --git a/crates/middleware/src/lib.rs b/crates/middleware/src/lib.rs
index 030ba306ea5..fad296093aa 100644
--- a/crates/middleware/src/lib.rs
+++ b/crates/middleware/src/lib.rs
@@ -1,25 +1,57 @@
-use std::{future::Future, pin::Pin};
-
 use alloy_json_rpc::RpcResult;
-use alloy_networks::Network;
+use alloy_networks::{Network, Transaction};
 use alloy_transports::{BoxTransport, RpcClient, Transport, TransportError};
 
+use std::{future::Future, pin::Pin};
+
 pub type MwareFut<'a, T, E> = Pin<Box<dyn Future<Output = RpcResult<T, E>> + Send + 'a>>;
 
-pub trait Middleware<N: Network, T: Transport = BoxTransport> {
+/// Middleware is parameterized with a network and a transport. The default
+/// transport is type-erased, but you can do `Middleware<N, Http>`.
+pub trait Middleware<N: Network, T: Transport = BoxTransport>: Send + Sync {
     fn client(&self) -> &RpcClient<T>;
 
+    /// Return a reference to the inner Middleware.
+    ///
+    /// Middleware are object safe now :)
     fn inner(&self) -> &dyn Middleware<N, T>;
 
-    fn send_transaction<'a>(
-        &self,
+    fn estimate_gas<'s: 'fut, 'a: 'fut, 'fut>(
+        &'s self,
         tx: &'a N::TransactionRequest,
-    ) -> MwareFut<'a, N::Receipt, TransportError> {
+    ) -> MwareFut<'fut, alloy_primitives::U256, TransportError>
+    where
+        Self: Sync + 'fut,
+    {
+        self.inner().estimate_gas(tx)
+    }
+
+    /// Send a transaction to the network.
+    ///
+    /// The transaction type is defined by the network.
+    fn send_transaction<'s: 'fut, 'a: 'fut, 'fut>(
+        &'s self,
+        tx: &'a N::TransactionRequest,
+    ) -> MwareFut<'fut, N::Receipt, TransportError> {
         self.inner().send_transaction(tx)
     }
+
+    fn populate_gas<'s: 'fut, 'a: 'fut, 'fut>(
+        &'s self,
+        tx: &'a mut N::TransactionRequest,
+    ) -> MwareFut<'fut, (), TransportError>
+    where
+        Self: Sync,
+    {
+        Box::pin(async move {
+            let gas = self.estimate_gas(&*tx).await;
+
+            gas.map(|gas| tx.set_gas(gas))
+        })
+    }
 }
 
-impl<N: Network, T: Transport> Middleware<N, T> for RpcClient<T> {
+impl<N: Network, T: Transport + Clone> Middleware<N, T> for RpcClient<T> {
     fn client(&self) -> &RpcClient<T> {
         self
     }
@@ -28,14 +60,22 @@ impl<N: Network, T: Transport> Middleware<N, T> for RpcClient<T> {
         panic!("called inner on <RpcClient as Middleware>")
     }
 
-    fn send_transaction<'a>(
-        &self,
+    fn estimate_gas<'s: 'fut, 'a: 'fut, 'fut>(
+        &'s self,
+        tx: &'a <N as Network>::TransactionRequest,
+    ) -> MwareFut<'fut, alloy_primitives::U256, TransportError> {
+        self.prepare("eth_estimateGas", tx).box_pin()
+    }
+
+    fn send_transaction<'s: 'fut, 'a: 'fut, 'fut>(
+        &'s self,
         tx: &'a N::TransactionRequest,
-    ) -> MwareFut<'a, N::Receipt, TransportError> {
+    ) -> MwareFut<'fut, N::Receipt, TransportError> {
         self.prepare("eth_sendTransaction", tx).box_pin()
     }
 }
 
+/// Middleware use a tower-like Layer abstraction
 pub trait MwareLayer<N: Network> {
     type Middleware<T: Transport>: Middleware<N, T>;
 
@@ -44,3 +84,13 @@ pub trait MwareLayer<N: Network> {
         M: Middleware<N, T>,
         T: Transport;
 }
+
+#[cfg(test)]
+mod test {
+    use crate::Middleware;
+    use alloy_networks::Network;
+
+    fn __compile_check<N: Network>() -> Box<dyn Middleware<N>> {
+        unimplemented!()
+    }
+}
diff --git a/crates/networks/Cargo.toml b/crates/networks/Cargo.toml
index 6af87d82e4e..70982c2425a 100644
--- a/crates/networks/Cargo.toml
+++ b/crates/networks/Cargo.toml
@@ -12,6 +12,7 @@ exclude.workspace = true
 
 [dependencies]
 alloy-json-rpc.workspace = true
+alloy-primitives.workspace = true
 alloy-rlp.workspace = true
 alloy-transports.workspace = true
 pin-project = "1.1.2"
diff --git a/crates/networks/src/lib.rs b/crates/networks/src/lib.rs
index 3fddb15a928..5eddd7744c2 100644
--- a/crates/networks/src/lib.rs
+++ b/crates/networks/src/lib.rs
@@ -1,6 +1,14 @@
 use alloy_json_rpc::RpcObject;
 
-pub trait Network {
+/// Captures type info for network-specific RPC requests/responses
+pub trait Network: Sized + Send + Sync + 'static {
+    #[doc(hidden)]
+    /// Asserts that this trait can only be implemented on a ZST.
+    const __ASSERT_ZST: bool = {
+        assert!(std::mem::size_of::<Self>() == 0, "Network must by a ZST");
+        true
+    };
+
     /// The JSON body of a transaction request.
     type TransactionRequest: Transaction;
 
@@ -11,10 +19,12 @@ pub trait Network {
     type TransactionResponse: Transaction;
 }
 
-/// Captures getters and setters common across transactions across all networks
+/// Captures getters and setters common across transactions and
+/// transaction-like objects across all networks.
 pub trait Transaction:
-    alloy_rlp::Encodable + alloy_rlp::Decodable + RpcObject + Sized + 'static
+    alloy_rlp::Encodable + alloy_rlp::Decodable + RpcObject + Clone + Sized + 'static
 {
+    fn set_gas(&mut self, gas: alloy_primitives::U256);
 }
 
 /// Captures getters and setters common across EIP-1559 transactions across all networks
diff --git a/crates/transports/src/batch.rs b/crates/transports/src/batch.rs
index bde8a1af714..42b37bd14b1 100644
--- a/crates/transports/src/batch.rs
+++ b/crates/transports/src/batch.rs
@@ -63,7 +63,7 @@ where
 #[pin_project::pin_project(project = CallStateProj)]
 pub enum BatchFuture<Conn>
 where
-    Conn: Transport,
+    Conn: Transport + Clone,
     Conn::Future: Send,
 {
     Prepared {
@@ -110,7 +110,7 @@ impl<'a, T> BatchRequest<'a, T> {
 
 impl<'a, Conn> BatchRequest<'a, Conn>
 where
-    Conn: Transport,
+    Conn: Transport + Clone,
 {
     #[must_use = "Waiters do nothing unless polled. A Waiter will never resolve unless its batch is sent."]
     /// Add a call to the batch.
@@ -139,7 +139,7 @@ where
 
 impl<'a, T> IntoFuture for BatchRequest<'a, T>
 where
-    T: Transport,
+    T: Transport + Clone,
 {
     type Output = <BatchFuture<T> as Future>::Output;
     type IntoFuture = BatchFuture<T>;
@@ -151,7 +151,7 @@ where
 
 impl<T> BatchFuture<T>
 where
-    T: Transport,
+    T: Transport + Clone,
 {
     fn poll_prepared(
         mut self: Pin<&mut Self>,
@@ -248,7 +248,7 @@ where
 
 impl<T> Future for BatchFuture<T>
 where
-    T: Transport,
+    T: Transport + Clone,
     T::Future: Send,
 {
     type Output = Result<(), TransportError>;
diff --git a/crates/transports/src/call.rs b/crates/transports/src/call.rs
index f76de8535f8..1beb02b0f88 100644
--- a/crates/transports/src/call.rs
+++ b/crates/transports/src/call.rs
@@ -12,7 +12,7 @@ use tower::{Layer, Service};
 #[pin_project::pin_project(project = CallStateProj)]
 enum CallState<Params, Conn>
 where
-    Conn: Transport,
+    Conn: Transport + Clone,
     Conn::Future: Send,
     Params: RpcParam,
 {
@@ -29,7 +29,7 @@ where
 
 impl<Params, Conn> CallState<Params, Conn>
 where
-    Conn: Transport,
+    Conn: Transport + Clone,
     Conn::Future: Send,
     Params: RpcParam,
 {
@@ -78,7 +78,7 @@ where
 
 impl<Params, Conn> Future for CallState<Params, Conn>
 where
-    Conn: Transport,
+    Conn: Transport + Clone,
     Conn::Future: Send,
     Params: RpcParam,
 {
@@ -101,7 +101,7 @@ where
 #[pin_project::pin_project]
 pub struct RpcCall<Conn, Params, Resp>
 where
-    Conn: Transport,
+    Conn: Transport + Clone,
     Conn::Future: Send,
     Params: RpcParam,
 {
@@ -112,7 +112,7 @@ where
 
 impl<Conn, Params, Resp> RpcCall<Conn, Params, Resp>
 where
-    Conn: Transport,
+    Conn: Transport + Clone,
     Conn::Future: Send,
     Params: RpcParam,
 {
@@ -129,7 +129,7 @@ where
 
 impl<'a, Conn, Params, Resp> RpcCall<Conn, Params, Resp>
 where
-    Conn: Transport,
+    Conn: Transport + Clone,
     Conn::Future: Send,
     Params: RpcParam + 'a,
     Resp: RpcReturn,
@@ -143,7 +143,7 @@ where
 
 impl<Conn, Params, Resp> Future for RpcCall<Conn, Params, Resp>
 where
-    Conn: Transport,
+    Conn: Transport + Clone,
     Conn::Future: Send,
     Params: RpcParam,
     Resp: RpcReturn,
diff --git a/crates/transports/src/client.rs b/crates/transports/src/client.rs
index 32f09197475..d7831275623 100644
--- a/crates/transports/src/client.rs
+++ b/crates/transports/src/client.rs
@@ -40,7 +40,7 @@ impl<T> RpcClient<T> {
 
 impl<T> RpcClient<T>
 where
-    T: Transport,
+    T: Transport + Clone,
     T::Future: Send,
 {
     #[inline]
diff --git a/crates/transports/src/transports/json_service.rs b/crates/transports/src/transports/json_service.rs
index 970e8ff82e3..e90f680df95 100644
--- a/crates/transports/src/transports/json_service.rs
+++ b/crates/transports/src/transports/json_service.rs
@@ -24,7 +24,7 @@ impl<S> tower::Layer<S> for JsonRpcLayer {
 
 impl<S, Param> Service<JsonRpcRequest<Param>> for JsonRpcService<S>
 where
-    S: Transport,
+    S: Transport + Clone,
     Param: RpcParam,
 {
     type Response = JsonRpcResponse;
diff --git a/crates/transports/src/transports/mod.rs b/crates/transports/src/transports/mod.rs
index 30db5d23a12..cf7fd6cd83a 100644
--- a/crates/transports/src/transports/mod.rs
+++ b/crates/transports/src/transports/mod.rs
@@ -6,22 +6,28 @@ pub use json_service::{JsonRpcFuture, JsonRpcLayer, JsonRpcService};
 
 use serde_json::value::RawValue;
 use std::{future::Future, pin::Pin};
-use tower::{util::BoxCloneService, Service};
+use tower::Service;
 
 use crate::TransportError;
 
-pub type BoxTransport = BoxCloneService<Box<RawValue>, Box<RawValue>, TransportError>;
-
 pub trait Transport:
     Service<
         Box<RawValue>,
         Response = Box<RawValue>,
         Error = TransportError,
         Future = Pin<Box<dyn Future<Output = Result<Box<RawValue>, TransportError>> + Send>>,
-    > + Clone
-    + Send
+    > + Send
+    + Sync
     + 'static
 {
+    fn erased(self) -> BoxTransport
+    where
+        Self: Sized + Clone + Send + Sync + 'static,
+    {
+        BoxTransport {
+            inner: Box::new(self),
+        }
+    }
 }
 
 impl<T> Transport for T where
@@ -30,8 +36,60 @@ impl<T> Transport for T where
             Response = Box<RawValue>,
             Error = TransportError,
             Future = Pin<Box<dyn Future<Output = Result<Box<RawValue>, TransportError>> + Send>>,
-        > + Clone
-        + Send
+        > + Send
+        + Sync
         + 'static
 {
 }
+
+pub struct BoxTransport {
+    inner: Box<dyn CloneTransport + Send + Sync>,
+}
+
+impl Clone for BoxTransport {
+    fn clone(&self) -> Self {
+        Self {
+            inner: self.inner.clone_box(),
+        }
+    }
+}
+
+trait CloneTransport: Transport {
+    fn clone_box(&self) -> Box<dyn CloneTransport + Send + Sync>;
+}
+
+impl<T> CloneTransport for T
+where
+    T: Transport + Clone + Send + Sync,
+{
+    fn clone_box(&self) -> Box<dyn CloneTransport + Send + Sync> {
+        Box::new(self.clone())
+    }
+}
+
+impl Service<Box<RawValue>> for BoxTransport {
+    type Response = Box<RawValue>;
+
+    type Error = TransportError;
+
+    type Future = Pin<Box<dyn Future<Output = Result<Box<RawValue>, TransportError>> + Send>>;
+
+    fn poll_ready(
+        &mut self,
+        cx: &mut std::task::Context<'_>,
+    ) -> std::task::Poll<Result<(), Self::Error>> {
+        self.inner.poll_ready(cx)
+    }
+
+    fn call(&mut self, req: Box<RawValue>) -> Self::Future {
+        self.inner.call(req)
+    }
+}
+
+/// checks trait + send + sync + 'static
+fn __compile_check() {
+    fn inner<T: Transport>() {
+        todo!()
+    }
+    inner::<BoxTransport>();
+}