I have seen a lot of postings with pictures of plastic coming out from between the sheer strips. Probably too late for that, so plan b would be masking tape and newspaper on the sheer line.

Whoa, hang on a second, you would be very likely to get your two halves glued together prematurely. Maybe you have to pull the halves apart and do them separately.

I think that is what flyfisher did:
www.flyfisher-kayaks.com/guillemot/guillemot.htm

Good luck

Pete