Air conditioner mounting

[Walker]

Mounting a new dometic air conditioner/heat pump on a 2007 diplomat.  Mounting bolts are to be torqued to 40-55 in/lbs to crush the gasket to 3/4".  Problem is, it draws the return grill bracket into the ceiling so far the grill won't attach.  There is nothing solid to draw against in the ceiling, just foam and the ceiling material.  Has anyone run into the problem or have a solution?

[Gary 05 AMB DST]

Matt, could you give some information on the model you used for replacement.

Thanks, 

Gary 05 AMB DST

[Walker]

Gary, sorry for the lack of info.  I originally had a penguin and am replacing it with a blizzard nxt h551816a.  

[96 EVO]

I just go by feel. Keep all 4 bolts equal.

[vito.a]

I think there were some steel crossbars the bolts go through.  

Did the bolts fall out and not get put back in correctly?

[Walker]

Ok, the opening in the ceiling has a metal support "box" lining the opening.  The rear of the opening has the ducts on either side.  There is no support framing around the ductwork.  The return air grill bracket is maybe 18 guage sheet metal with support running along the front and back, nothing on the sides spanning the duct openings.  I took some 1x1x1/8" aluminum and riveted it to the return grill bracket.  Worked out good, bolts are torqued, gasket is set.