While digging through the piles of stuff in the garage I came upon a box of self-adhesive bicycle tube patches. They're roughly 1" square, black, rubber (or composition) with adhesive backs. I guess they're about 1/32" thick. I traced the mpc shape onto a patch backing paper, trimmed the patch to shape and stuck it on a mpc. Almost perfect but a little thin, so I stuck another one on. Its a lot better than electrician's tape IMO and a lot cheaper than buying a package from a supplier.