Dometic roof are motor shot. How easy to replace?

I can get the unit on the roof no problem. As long as hookup is the same as the old one it shouldn't be a big deal. The 13.5 cools ok but takes awhile. I have a RV Guardian 6500 generator so that would be my only concern is running both a 13.5 and a 15k at the same time. It gets in the 110's here easy in the summers...