Not sure of your vintage but most AC units are held down with 4 bolts accessible once the ceiling shroud is removed.
Remove the ceiling shroud and you should see 4 bolts that go up to the unit. Since the AC units were not made for Airstreams they sit on a plastic pan that follows the curve of the roof and presents a flat surface for the AC to sit on.
The hard part is going to be the drain hose. It is in there tight and has very little room to move it off the drain pan. Don't cut it or you will have trouble when replacing the unit
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles