We have 2010 Jayco outback hawk and have fitted a Dometic 2.2 in the roof, we brought the airconditioner from a Sydney dealer for $1980.00 del to Dubbo and brought the aluminium support from the jayco dealer, if I was doing it again I would get the alum support made up at a welding works, it would only cost about half what we payed. we were quoted $3200.00 to fit the same unit in Dubbo. I bent the alum support to the same shape as the roof, the dealer said they didn't do that just put it on and screw it down, I am sure its better to shape it to the roof. I fitted it myself wasn't hard to do including the wiring, we haven't used the cooling yet but have used the heater it works well. When the roof is up we use a support on each corner which is a piece of 20mm tube at the front and 25mm at the back, just light steel tube cut to the right length and with rubber stoppers on the ends, hope this helps,
Ken