I like to pre-cook my boats before final sanding and varnishing. I wrap it in black plastic, and stick it out in the sun, rotating it every couple hours. On a sunny day, I can get the air temperature inside the boat above 100° F by doing this.

I started doing this after noticing that new boats left out in the sun will get weave print-through in the varnish, where older boats do not. Epoxy continues to cure long after it is hard and dry. Heat speeds up the cure and hardening.

I have noticed that the boats where I did this cooking do not show problems with the pock marks. This may be due to no stress in the glass, but maybe the cooking makes a difference.

By doing the cooking before the glass has set up really hard, it gives a chance for the epoxy and glass to relieve stress while everything is still malleable. The heat during the cooking will temporarily soften the epoxy allowing the glass to move. Since the epoxy is still relatively green, this movement doesn't break the bonds.

I am also doing this cooking before doing any significant sanding. There are no places where I have tagged the high spots of the glass, thus introducing a little localized weakness.

Another difference with wrapping in black plastic is, the heat is less of a surface effect. Sun on a hot deck will heat the outside surface a lot faster than the inside surface. This introduces its own stress on the lay up. If this is combined with existing stress, it might cause more of a problem. By wrapping in plastic, the inside and outside do not experience as big a temperature differential. Maybe this lets the stress be relieved more gracefully.

Just some thoughts. I suspect there are no simple answers to the problem. I have had good success sanding into the wood without leaving a halo, but I can't explain why.

BTW, the pre-cooking for print through seems to work a little bit.