Air Conditioner Inside Mounting
My coach has the original roof mounted A/C unit. The interior shroud is discolored and a bit brittle, so you have to be careful when removing the shroud. To remove the plastic, turn the two plastic thumbscrews to release the center section (it pivots down and out). Next remove the screws from around the perimeter. Finally remove the single nut in the center of the unit. The shroud should come off easily.
This is what you have when the shroud is off.
With the headliner down, you can see the framing and cross members. The A/C is held in place by a series of clamping bars and bolts seen in the four corner areas. The A/C does not need to be removed to replace the headliner.