[Shane826]

Ok I just had that all apart to install my new Atwood A/C. The plastic piece you are pointed to is just a plastic shell. It is siliconed to the roof. Precision, you say? Not on mine, it wasn’t. Anyway, the plastic shell has a 13.5”x13.5” cutout with a raised lip for the A/C to blow thorough. The gasket Travis (FlyBoyTR) is talking about goes around this cutout, between the plastic shell and the A/C unit.

Below that shell is the actual riser. It’s made of a piece of TM foam & aluminum sandwich, with a similar cutout for the A/C to blow through. Then it is raised with a frame made of either wood or PVC board 1”X2”. The riser is sealed and screwed to the roof, there was a bead of silicone around the opening between the shell and riser, with the foam gasket and A/C on top of the shell.

So what’s the purpose of all this? In most RVs the A/C control unit is just mounted to the ceiling. That won’t fly on a TM because when you close the camper, the control unit would get crushed between the overlapping shell roofs. So TM came up with this system to allow the control unit to be recessed into the ceiling.

I attached some pictures from when I had it all torn apart. First two are the shell, last two are the rebuilt riser.