How have you sealed the trap door on your fastback to minimize noise and odors from entering the cab? Also I have speakers in the trap door, so they also need to be sealed too.
I was thinking the same thing, but maybe some closed-foam weather seal. The corners, transitioning from the fold down seat to the trap door, seem to have the biggest gap and maybe tough to seal.
Go to mcmaster.com and look at their adhesive-backed foam tape. Look at page 3415 for starters but search around the site and you might find something else. We use the stuff at work but I don't have any part numbers handy right now.