I have to admit, I might not have built them if I had to pay the price
for the marine ply. Since then, I have found how much I enjoy them so
wish I had paid the price. However, regardless of his position of
bathroom underlayment, I have learned a lot from William's posts.

FINALLY, got all the paint removed from the bottom of #1. For most of
it I just used a sander and that was a lot of work. Then I remembered
"Paint Remover" and went and bought a spray can of Citrus Strip (or
something like that) in a spray can. It sorta worked and at least
seriously lessened the work. I still had to do final removal with the
sander.
Now, I am ready to apply a coat of epoxy and lightweight glass.