[Christ]

If I had a mobile home, I'd be going for max mileage, myself. It's a second nature, for me.

The 5 speed swap isn't really that hard. As long as you have 1/2 an idea of what you're doing, it's a pretty simple process, really. If you're going to go that far, gear changing will probably net you some more MPG's as long as you're not short on torque as it is.

As far as wheel skirts, go, just about anything will work... in fact, the easy way would be to get some thin aluminum (I presume your camper is aluminum) and use the wheel trim as a template to cut it out. Leave about 1/2" all the way around the wheel trim line, then screw it in with some sheet metal screws. Pull it back off, run a bead of caulk around the wheel arch and where each screw goes through. You could also use some plain old rubber weatherstripping.