jmac, I have the exact same fifth wheel as you and I am trying to answer the same question. My previous fifth wheel was a toyhauler and had an Onan 5500 in it. I did not use it much but when I did it was nice to have it built in. The trouble I had with it was I had to clean the carb a number of times due to lack of use, my fault. With the unit being a toyhauler I was not concerned with the loss of storage.
Now that I have a unit just like yours, a built in is not possible without loss of storage. Here are a couple options I am looking at.
http://www.pplmotorhomes.com/parts/onan-generators/2000w-yamaha-gen-kit.htmTwo Rybois with parallel kit
http://www.homedepot.com/p/Ryobi-2200-Watt-Gasoline-Powered-Digital-Inverter-Generator-RYI2200/203617901?N=bx9nhttp://www.homedepot.com/p/LIFAN-3-600-Watt-Energy-Storm-9-HP-270cc-Inverter-Gasoline-Powered-Generator-ESI3600iER/203369836?MERCH=RV-_-RV_gm_pip_rr-1-_-NA-_-203369836-_-NAs you can see the prices vary. Either option will handle on AC unit. Quietness is a big factor. I do not see myself using a generator often or for extended periods of time. That is why I am leaning toward the less expensive models. Another consideration is, can I turn off the fuel and let the unit run out of gas so there would be no residual gas in the carb?