Of your various problems, the only one I really see an improvement in is the room in a fiver vs. your MH. The towing, buying gas, height of bed, etc. are not going to get any easier if you switch, IMO.
On the flip side, with a fiver you will be dealing with more difficult hitching and setup at camp, no restroom and kitchen in your main vehicle, and less room for the pets. We've had two fivers and there is a lot to like about them. But I'm not sure they are going to help you very much. Other than living space.