What type to buy

Buy your last coach first.

Time spent in the archives of this site will tell you much about which brands to consider and which to avoid. I strongly suggest if you find a unit you want to buy spend some cash and have a qualified, non biast, service3 center check it over. This can save you thousands down the road. Best of luck and have fun

if you are doing more sitting than driving, you really have no need for a diesel.
$80,000 will buy you a much nicer/newer gasser than a diesel. as long as you are towing only 3,700 lbs. a gasser will work just fine.
bumpy

My 2 cents over 36ft. go Dsl. if under 36ft. go gas!!! rvtommy

Shop a floor plan first. The lay needs to support your intended life style. Spend as much time as possible without a sales rep in various configurations going thru what your daily routine will be. Is the kitchen big enough for your normal meal prep? Does the bathroom fit your needs. Could you go a few days inside the coach and not feel like the walls are closing in if the weather is poor? Is there enough interior storage for your day to day needs?

Both the modern Ford and Workhorse chassis will tow up to 5K lbs without a problem as will a diesel powered coach. The diesel will bring additional amentias that will help make the coach more comfortable both at a CG or going down the road but at a bit higher initial cost for the diesel chassis. If your long range plans include a lot of road time a diesel might be better. Do a test drive in each before making a decision and don't let high fuel prices scare you. The true number is cost per mile and you only need a gain of about 2 MPG from a diesel to offset the pump price difference for gasoline.

We travel from Florida mostly out West and have had no problem towing our 3700 pound toad over any of the high mountain passes with our gas powered coach. We very seldom take a "local" trip and most of our journeys are for several months and several thousand miles and the gas coach serves us well. I have owned several diesel and other gas powered coaches and always pick the coach that will serve us the best today. Through the years we have learned that we spend more time parked than we do driving. For that reason, the floor plan is the most important.
What you are asking about towing a 3700 pound toad over mountains is just a simple feat that any of the gas or diesel powered coaches can accomplish without any hassle at all. Find the floor plan that suits your needs and don't worry about the engine.