I put a Coleman Mach 8 cub 9200BTU in our 5th wheel in April. The hard part was getting the unit up on the roof (87 pounds) but thats what a son is for and taking out the old vent.
Really wasn't that bad and like you the wiring was already installed.
The new unit only takes 11 amps and really cools the bedroom and bathroom area down in a hurry.
The 15000 AC that came with the camper just doesn't cut it when traveling most of the day in extreme heat.
John, Jan & Buddy
2012 Chevy 2500HD LTZ Duramax CC 4X4
2013 335SS Cruiser Patriot
I got my coleman Mach 3 (with all parts needed for install) off the internet. Was WAAYY cheaper than the dealer where i bought my TT. However, I had them install it and I think they charged me 275.00. That included them "throwing in" a thermostat. Tstat was super cheap, but all wiring was intact. Looking back, Id pay that in a heartbeat, especially considering if you compromise your roof in any way, 275.00 wouldbe on the cheap side for any repairs!