Well- first recommendation is to install a couple decent solar panels on the roof. Dpending on where you camp- I thin you will find many find that type of generator superior to the fossil fuel kind.
For a bumper cargo carrier you are going to want a receiver hitch that is bolted/welded to the frame to ensure it doesn't come apart at some point. You should also consider the weight of the generator. I notice a difference in how the trailer handles when I just have a bike carrier and a couple of bikes back there. That said- many have done it and if you do a search for cargo carriers, generator mounting, etc....Im sure you will run across many posts where it is discussed. Good luck
Rick