Well, I should have read all of the posts before posting. Seems you all have already hit the black plastic sun thing.

Sam Devlin talks about print thru and how he handles it in his book "Devlin's Boat Building". He did a tempature test at 92 degrees F, he took surface temp of boat with dark blue paint, it was 142 degrees, an off white was 113 degrees. He uses West system, and says the resin can have a heat deflection temp of about 125 degrees F. That is the temp at which cured epoxy begins to deflect, or move, under stress. At 150, the epoxy begins to act like a rubber compound more than hard epoxy.

He uses 4 oz cloth for a really good finish with little print thru and recommends 6oz or less. The heavier glass will print thru much more.