Polyester is not going to stick to pressure treated wood very well.
Also, no matter how old it is if you only cover the top the two surfaces
will still swell and shrink at different rates causing the boards to cup
again. When the glass cracks it is going to produce sone nasty places
to stub a bare foot.

About 20 years ago on Lake Sinclair I built a 10'x16' floating dock/swim
platform with PT pine 4/4 decking over a 2x8 frame leaving about 1/8"
gap between boards. Painted all the parts before assembly with
stainless deck screws. Corners were reinforced with short lengths of
6x6 angle iron. Covered the top with dacron canvas tacked around the
edges and covered the edges with plastic dock bumper strips. The dock
is still there and looks good although I don't own it any more. To my
knowlege the cover and bumpers have been replaced twice and the
styrofoam floats once.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com