it all depends on your usage and needs...
You can get a 5.5 Onan installed for around $5,000.00 if you already have the generator prep kit on the trailer....
OR you could go with twin Honda's with a parallel cord.. I do that with my fifth wheel and can run 15K AC and a bunch of other stuff at once..
The downfall if fuel... You may want to look for an extended run tank to help with fuel usage...
I am switching from the twin Honda's to a 6.5K Onan in the next few weeks , I like the idea of just pressing a button and having electric.. Getting the others out and set up to use was getting old.