Our neighbor has a 32' gas, his coach weighs about 2/3rd of our Newmar 40', he gets an average of 6-7 MPG, I get average 9-10. He has a tune up nearly every year at about $1000 per visit to the dealer. ( air cleaner, plugs and wires, oil change, fuel filters etc) They spend about 30 nights per year in their coach. Our Newmar has a gauge to tell us when the air filter needs to be changed, 43K miles it is still running in the green, and it is cleanable. I change my own oil at 10K miles, 24 qts, Delo-15/40, Fuel filter at 10K miles at 40 bucks each, Most coaches will run a lot longer than 10k on filters.
They bought their coach new, we bought ours used, they paid double what we did. they like our better :)
Hill climbing, the diesel does way better. Shell Canyon is the only hill we've found we could not keep up with traffic, it's just too crooked.
Bottom line, buy what you like, learn to do the simple maintenance your self. And remember each coach will be a study in its self.