We put a couple of Mitsubishi split systems in some temp studios a while back. In that service they worked well, hooking the precharged lines wasn't a problem. They might of spit a gram or two of refrigerant out at connecting, but held up well thereafter. I wouldn't use that kind of system in a coach for several reasons. They're relatively heavy. They're bulky, both outside unit and the evaporator. In a space limited environment (GMC) they take too much room. They aren't as tolerant of poor power as the RV units (Take a look inside one - there are several tricks played to make it tolerate sagging or blooming voltage without damage. There are also some you can't see.) They won't be as tolerant of vibration either. Their benefit is, they're quiet. They're probably a bit more efficient than the RV units, but that's not really a concern in RV use. My thought is, the time and effort would be better spent ducting one ot two of the roof mount units, which ought to shut it up considerably - noise being the only real drawback to them. A bit of thought and finagling should produce ductwork which fits in the ceiling of a GMC.. or at least is very wide and not greatly deep.

These coaches spread with only the weight of the roof itself over time. Increase that, they will spread more. With the walls out, I can see where one might take either of two approaches. Some curved stanchions in the walls - I'd do three to a side - could be carried through the floor directly to the coach frame. Alternatively, careful placement would allow straight ones to run up through the cabinetry at the wall. Put about a 4x4 inch block on top bandsawed or milled to match the roof curve. Then on the outside do the same with your 'patio' supports, and through - bolt these pads. Now you've got the load carried through to the frame and as an added benefit, you've support holding the roof up if you crossbolt the stanchion to the roof ribs. No more spread at all at this point.

The weight of the patio is to a degree going to affect the coach's handling, the amount of affect related to the weight of the stuff and how high above the roof you raise it. It'll look cool as hell, though.

--johnny