Get something with an Aqua-Hot. It's a diesel fueled water heater that gives unlimited hot water. But your biggest problem won't be heating the water, it will be getting the water to heat if you're boondocking.
I recommend a very well used Prevost. In your price range, you can get a professional conversion with the 8V92 engine. I don't think you can get the Detroit series 60 unless you add a few more bucks. ;)
Although it is an electric coach, we can run ours for about 2 days before we have to run the generator to recharge the batteries. Fresh/gray/black tanks have excellent capacity too.
Edited to add: just saw the screen name of the OP and remembered he is going to finance his RV. This option is not readily available for those who do not have cash.