If it is good wood, show it off. I'd do this:

Quarter-round the sides which will be on the edge of the platform.
Drill the screw holes
Use a low viscosity epoxy on the planks to seal the wood, concentrating on
the end grain and screw holes (just don't fill them up). You can leave the
bottoms unsealed to let the wood breathe.
Sand between the epoxy and all varnish coats, of course.
Varnish with an outdoor/marine varnish.
Mount with stainless screw or bronze nails if you are really going for the
nautical look.

Glue the floats on with foam caulk. It fills gaps, sticks like crazy, and
is compatible with Styrofoam.

If it isn't pretty, I'd make a fiberglass "shower cap" like a Tupperware
lid:

If you are going to cover it, why not just use plywood and save your lumber?
Either way, here is a method.

Assemble the platform top, cover it with plastic, then cover it with glass
and enough resin to just wet out the cloth, leaving a non-skid pattern.
After this sets, use a roller to apply gel coat. Trim the edges and voila!



"John" wrote in message
...
You will be glad to know I have given up on the idea of fiberglassing the
swim platform.

Now I am thinking about using a polyurethane paint intended for truck
bedliners. The manufacturer says it will accomodate the wood movement
just fine, but recommends I use a primer first because it doesn't still
all
that well to PT.

Thanks.