Need to improve a RV with a big block

[427v8]

Hi,
My daily is pretty good, I have a motorcycle, but I have an RV, it gets like 9 mpg.

We are taking it out west and plan on putting on 3600 miles.

Now, if I can improve it's gas milage by just 2mpg the gas savings will be huge!
It has a 454 chevy V8, with TBI fuel injection and a 4 speed auto trans with torque converterlock up.

Any ideas on how to improve the gas milage?

Use a wideband O2 to run it leaner?
Improve the exhaust ( headers etc)

Any other tricks?

thanks
Keith