454's have heat problems, crank problems, 454 problems. Big blocks are usually only in big motor homes as Terry's is an exception in a class C. Carbs are what they are and only get between 6-8 on a good day and drop to 4 quickly but TBI fuelies are not much better than carbs except when it comes to driving in mountains as they at least account for that. Late 90's 460's are MPI so are better but they are still big block gassers pulling lots of weight, I got 6-9 out mine running to Florida and back but that was through the mountains both ways. The V10's are 5.4's with 2 cylinders added on but they seem to do all right as they are a newer motor style which because it is designed to getter better emissions also produces better power. I have a friend that claims 10-12 mpg (I have never verified) out of his 38' with 3 slides which weighs 20500 unloaded but can only carry 1500lbs of cargo including people. What is interesting that one of his buddies 1-ton with the V10 apparently got 2 mpg less towing a big 5th wheel and Dirks old built 460 got better fuel economy as well towing his 37' 5th. my dad has one in his 29' B+ with 3 slides and gets similar mileage and probably a gross weight of only 16000 lbs.
Oh I just noticed the size you were looking at, hmmm so V10 will be your best choice but hard to find in that price range. B's are vans and if you are fine with confined spaces they are an easy way to travel. B+'s are relatively newer and pricey as they mostly depend on slides. C's are good as long as you don't buy a great big one, they typically more than any motorhome always overload the chassis. If they get too long all that is holding that huge overhang on is some welded channel which is not conducive to towing a trailer, flat tow is better with no weight on the tongue.
You know diesels, better power, better fuel economy, theoretically less maintenance but a 7.3l requires 16 l of oil for an oil change at roughly the same intervals as gas. If I had to choose a reasonably priced C it would probably with a 7.3 l but of course those have their own set of problems and of course diesels in general are more expensive to fix. Towing a 30' light weight travel trailer years ago yielded me 14 mpg through Vermont hills. Just as a reference my 26700 lb motorhome got 12 mpg to Burlington Vermont on one of the few times I didn't tow anywhere.
