Dan,

Back in the dark ages (almost 40 years ago) when epoxy was $40 an oz.
(or so it seemed) one of the first rules I learned was "never put
polyester on epoxy". Because of the cost back then almost no one used
epoxy for boat building or repair. This caused us to use poly in
adhesive applications that it was not very good at. I can vaguely
remember roughing up a surface for poly with something like a 26 grit
disk and then going back with a box knife and scoring the surface. You
never laid glass on a surface that had been painted. No matter how much
you sanded the poly just wouldn't stick and when I glassed new plywood
the first coat was thinned with styrene 30 to 50% to ensure a decent
bond. And of course you couldn't glass over planks because the tensile
strength of poly was too low, the glass would break at the seams when
the wood swelled. On top of all the above, it took a lot more poly to
do the job.

Life is so much easier since epoxy got relatively cheap.

Ron