I have found that when (long trips)fully loaded(minus 1/2 water tank) doing 65 mph on flat land we can get about 8-8.5 mpg. If I feel speedy and do 75 it drops to about 4.75mpg.
We took it slow going over,through and around the big hills in Colorado last year and averaged around 6-7mpg. That's full to the gills for 2 adults and 4 kids plus to big dogs.
We took a weekend trip to Omaha and averaged closer to 9 mpg.
All this time my autoparkbrake was slowly squeezing the driveline brakes but never felt it. Anyway Roger Haag talked me through the fix and it runs smoother now so I expect to stay around the 7-9mpg range.
If you have the P30 chassis send me a PM with your email and I'll send you all the info Roger sent me on your braking system. Also, make sure you look in the files section of the IRV2 website- I uploaded the generator manual, all wiring and plumbing schematics and will soon scan all my chassis manuals and other docs.
Ron

Join the Fleetwood Owners Group and Texas Boomers on this site. Let me know if you need documents for your rig if it's a P30 chassis

Ron,
I have a 1993 Pace Arrow with a 454 just wondering how many miles per gallon are you getting with your rig?