If it were me I'd remove the deck lid, place it upside down on a soft surface (table with a blanket..ect) and glue the weatherstrip to it with the 3M super weather strip adhesive that is black. I drilled 2 very small holes in the deck lid and hinges before I removed it so I could perfectly re-install it by matching the holes each side with an ice pick. Let it sit for a day then re-install the deck lid and it will shut like you've never heard before Good luck and be patient/ careful with the glue. Take your time and you'll be happy with the results. Refer to the Osborne Cougar Shop manuals if you don't know where the gasket goes exactly. If you do not own them...buy them!
as stated , take it off---put 3/4 masking tape where the seal goes and then another strip of tape out side the first lap----remove the first lap and this will keep you from getting any glue on the paint