For the small block owners (273, 318, 340, 360):
The combination of an Edelbrock 4-barrel intake and carburetor is just about ideal for motorhomes. If you stay out of the secondaries (!!!), you'll get slightly better gas mileage. The Carter/Edelbrock 4-barrel carburetors have smaller primaries than the old Carter BBD 2-barrel carburetors, In a nut shell, the BBD (and other brand) 2-barrel carburetors had/have to be sized for the maximum engine demand. The primaries on 4-barrel carburetors are sized for typical (cruising) demand and the secondaries kick in when the demand goes up (during acceleration and hill climbing).
Remember, you're driving a big truck, 1-ton or larger. If you want sports car performance, you're in the wrong vehicle. Also, steady, gradual acceleration -- like most sensible truckers use -- is much easier on the gas consumption.
Dual exhaust, especially sized correctly with an H- or X-crossover, will improve performance and fuel mileage. If you want to try headers, find a set of Tri-Y headers. Most of the ones on the market are designed for power at lower RPMs and better gas mileage, which is just what a motorhome needs. They're out there but kinda hard to find and usually have to be special ordered.
Do not, repeat DO NOT, use performance headers of any kind! The stock OEM exhaust manifolds are actually better for motorhome applications. (Almost all headers, except Tri-Y, are designed for high RPMs that you'll never reach.)
An air intake hose from the air cleaner to a source of cool air, like modern vehicles, will also help. (I'm getting older and forgot what they call them ... cold air induction?) If you have a fancy, aftermarket air cleaner, throw it away and get an OEM air cleaner or something similar.
Another trick is to use one or two boat bilge blowers to pump cool air into, or suck hot air out of, the dog house. The carburetor (and fuel) needs to be kept relatively cool for best operation and most doghouses don't provide enough air flow.
