You could always add a built in genset to an RV that has no generator prep. A member on the Ford Forums just did it on his 5th. You need a transfer switch, start/stop switch and wiring, and someone to fabricate the generator mount in the front storage area. If you're not handy, I'm sure an RV dealership would be able to do the install for you. Of course, this is contingent on there being enough room in the front storage compartment for the unit. The guy who did it on the forum bought a used generator and converted it to LP but you can get a new Onan 5500 LP unit for under 4k. Here is a link to the install thread.
5th Wheel Genset install...Here is the Onan 5500 LP gen:
Onan 5500 LP