Since no one had any help, I'll offer what we did, in case anyone might need the info.

Getting the carpet adhesive up was a monstrous task...and I spent many an hour cursing the previous owner who put the carpet down. What a stunningly foolish thing to do.

Anyway, adhesive remover, wire scrub brushes, and lots of rags. Went over each area probably 4-5 times, but got it 98% back to the original gel coat.

The Permaflex (by Sani-Tred) went on like a dream, and is a great surface. Water beads up. It's hard, so deck chairs with hard plastic feet slide around. But it sealed up all the tiny cracks in the gel coat, and seems like a good surface.

The only drawback is the amount of labor to produce the fairly exacting surface that the Permaflex has to go on to, to bond with the fiberglass. We didn't dare take any shortcuts (which was probably a good idea), and it sure looks good now (as does the garage floor, which we painted with the Permaflex we had left over.