Armstrong A/C, roof caving in

[bmklawt]

Took the center ceiling panel out today and noticed the roof is bowing in under the A/C unit, Armstrong TR21-12.
I also noticed that all the supports running between the ribs are one piece except under the A/C unit there two pieces.
Surprisingly this does not leak.

Been reading previous post on the subject and just want to make sure I get the repair right.

1, Are sheet metal screw into the exterior skin the only thing holding this down?

2, Is there a gasket under the unit or caulk or both?

3, How do I seal it when I put it back on? I've read Andy at Inland say Airstream used Vulkem, others have said there was a gasket.

4, Olympic rivets or screws again when reattaching?

5, How should I reinforce the ceiling? I'm thinking a 1/4" aluminum angle running front to back between ribs

6, Do I need additional support side to side?

7, What should I do or have done to the A/C unit while it's off?

8, What other questions should I be asking and/or what else should I be doing?

Thanks for the help

[goransons]

you can buy aluminum extruded C channel at most any metal supply shop that can be used to fill this space and provide support for the interior and exterior skin. I don't know specifically about your model AC, but I know that others I have worked on don't screw to the trailer, but instead are bolted through to the inner control unit with long bolts through the 14x14 opening, sandwiching the gasket against the trailer. Granted I haven't worked on to many air conditioner units, so can't claim to have seen it all.

[Silverwanabe]

I thought all the Armstrong AC's were riveted to the outer skin , not screwed in ?

[Aerowood]

You are on the right track with installing a froward to aft additional stringer. However, .250 is a little overkill. If you can find "C" channel the outside dimension is 1.750. If angle is used .125 will work, if "C" is used then .0625 will be fine. Be sure to tie the ends to the frames with a clip

[TomW]

Originally Posted by Silverwanabe

I thought all the Armstrong AC's were riveted to the outer skin , not screwed in ?

My Overlander's outer unit is screwed on with "RV putty" originally sealing the interface. The inside unit is riveted.

Tom

[bmklawt]

When I add supports either angle or channel between the ribs, do I need to rivet the skin to the support.

Would there be enough movement between the skin and new stringer to wear through the skin if not riveted.

Also do I need a gasket or will Vulkem do.