Pygmy sends a long 4"-wide strip of mylar with their kits for a similar reason: you butt 2 panels together, lay 2" fiberglass tape over the joint, saturate fully with epoxy, cover with a portion of mylar, and weight it down while it cures.

This method works pretty slick from an application stand-point, but I have some color mis-matches because of it. The wood panels were bare with the exception of these butt joints, and when I did the full hull epoxy job 2 or 3 weeks later, the rest of the hull didn't darken as much as the butt jointed areas. I have dark bands about 5" wide around each butt joint. It p#@$'s me off because I did it exactly per the instructions, had no problems with the epoxy, yet still it gets screwed up. But enough venting -- I'm working on boat #2 now a stripper...

Dean