Do you mean the exterior Decor Package trim panel?
Mine didn't have any gaskets, only a little strip caulk around the fasteners.
Also should mention a common error is to have the red area color too light; should be more of a maroon.
Kind of matches the shade of the unlit tail lamps.
My Decor Group '68 I'm using for reference was an original car, untouched original everything.
Same here with my '68's trunk "finish panel" nothing but some white caulk as I think a sort of thread lock for the stud nuts IIRC. Also totally agree with the maroon/dark red color for the finish panel. I'm still mad about how some "pro" restored it after talking, sending emails, photos of 3 original finish panels and putting notes in with the panel that I sent it to him. It came back lighter maroon than I requested and to top it off he could see right away when he got it that it was DARK MAROON and almost an exact match to the tail lights
