Some good ideas given above. If you want to use the portable, just use the old generator compartment for a place to carry your portable and fuel can. Then set the generator out on the ground to run it.
Another idea is to check on ebay for a used Onan, then install it permanently in your RV. I like the permanent set ups as they run off the RV's fuel supply and can be started and shut off from inside. Plus they are more secure and don't have to be locked away when you leave for a while.
I have a Honda 2000i and it is a fine generator, but I still prefer to just hit the start button inside to fire up my generator to make a cup of coffee, etc. My truck camper has a LPG 2.5KW generator permanently installed. While I don't use it often, it is handy when I want to do so.
A sliding tray as mentioned above would sure be nice on a portable unit, down side is still having to go outside to fire it up. Sure wish my wife showed more interest in going outside to fire up the generator when I need a cup of coffee or want to run the microwave. But she is a city girl and I never thought to check with her on that before we got married.
Another nice feature of the portables is you can move them away from your rig and run a long extension cord. Your neighbors may not like it but that is another issue. LOL :)