I will be adding a 2nd AC to our Class C soon. We are not prepped for 2nd AC (no hidden wiring ready for the unit) but will be using the vent above the master bed. The bedroom is always 5 to 10 deg hotter than the rest of the unit...just the way the layout is and the fact we have 1 vent, the last one on the line, coming to our bedroom. FYI -- I will be running an external plug and using the 2nd AC only at the campsite on those super hot/humid days. It will not be able to run off our genset in the C.
Point is, the suggestions so far are all good....esp. the part about lots of youtube vids. There is one out there with a guy doing EXACTLY what I just said...conduit hiding wiring to external plug for occasional use. I think the hardest part is going to be getting the unit on the roof...and the suggestion of ropes, plywood as a sled is right on.
Once I'm on the roof of my unit, I plan on having the extension ladder EXTENDED further to make the slope "less" so i'm not pulling the AC unit straight up.
dpglifestyle also says leave in box to pull up on roof -- something I had not considered...but will be since it will have a "built in sled" via the box.