65will and cwf. Thank you for your reply. I'm not sure why, but I did not get notified when you posted. If I had read your suggestions I would not have removed my middle vent today... Bummer.
Now I have the middle of the 3 vent curbs removed and I was planning on putting my AC in this weekend. After reading this I changed my mind. Makes sense - I can't compress the seal without having the inner skins in.
I've attached a pic of another situation that I have. The PO had installed really nice flexible solar panels on either side of the vents. The problem is the compression gasket will overlap the panel preventing me from an ideal seal (gasket to aluminum).
Do you think slightly overlapping this gasket and sealing with trempro will suffice? If not I will have to remove both panels.
I'm attaching a pic.