: I have had good luck using 3M Super 77 Sparay Adhesive (at any big box
: building supply). I would try it first with just a good solvent cleaning
: of the gel coat, you may not have to scratch the deck with sandpaper.

Cleaning the surface should be enough and any contact cement will work. Just make sure to double coat the surface of the Minicel. The first coat will soak in and seal the surface, and the second coat will provide a strong bond. One coat on the non-porous deck should be enough.