I have a 5th wheel now, but when I had my Kodiak 242RESL travel trailer, I had a receiver hitch welded onto my TT rear and I bought the GearDeck17 to carry my Champion 3100. It runs my 15K A/C just fine. This youtube video shows a guy with it mounted on the back of his 5th wheel. I thing the video covers all the bases. The enclosure is made and sold by a company in Colorado (google it).
Gear Deck 17 videoThe GearDeck is nice because when you get where you're going, it's designed such that the whole enclosure slides out about a couple of feet from the bumper. You don't have to lift the genny out to run it.
Then you can also prop the lid open and use it in that stance to be cover to shed from rain while still having sufficient air circulation. Only thing I would do different, is I wish the remote start version of the Champion had been available when I bought.