I recently installed a 5500 in a non-prepped unit. If yours is prepped it’s really not too difficult. Hardest part will be putting the generator in the compartment. It was pretty easy for me, I put the generator on a small dolly, lowered the front of the camper, then just slid the generator in.
Since I had to put the “prep” in myself, I was fully prepared with the wiring and propane connections. Had a local muffler shop make an extension pipe for the exhaust, and I boxed out the compartment with heavy gauge sheet metal. Since yours is factory prepped the only thing you need to do custom is the exhaust.
Karl - Southeast, NY
2020 377 RLBH
2018 Ram 3500 Mega Limited 6.7L Cummins w/ Aisin