In and of itself, gas vs. diesel makes relatively little difference. Things do get a bit confused because nearly all diesel motorhomes are pushers (rear engine), while nearly all gas motorhomes have the engine in front.
A front engine class A often shares some of the disadvantages you have of a class C (the doghouse space and heat issues), though often to a lesser degree than most class C's. The Ford E-series chassis is none to spacious in the driver's compartment. A rear engine class A does not have these issues, of course.
Do consider the tradeoff of a readily usable driver's door when parking or refueling. A great many class A's don't have a driver's door, and many that exist are rather more awkward to use than a class C driver's door.