I have my A/C out for roof repairs at the moment. What everyone is saying is correct. Four lag bolts which are secured from the inside of the camper, thru the plenum, but NOT thru the plywood roof. If you can picture this, the A/C unit sits up top over a square hole, from inside the camper there is (in my case) a metal plenum which sits under the same square hole. The four bolts go thru the metal plenum, up thru the square hole (not thru the plywood) and screws into the A/C unit up top. As you tighten the bolts, the plenum and the A/C unit get squeezed together like a sandwhich in a vise thereby squashing the foam seal on the bottom of the A/C unit creating a good seal against the roof.....gotta love those CH-47 guys at Fort Lewis with thier "Gutentight" torque LOL!
