Hi Charles.
If you fibreglass only one side you are looking for trouble methinks. If I were you I would heat the fibreglassed side and when hot force it back to the right shape. Then I would fibreglass the other side. Then the forces in the lid would be more balanced and the warping should stop.
JohnK

: I cut out my hatches on my Pygmy Osprey last week and fibreglassed the
: bottom. I'm using the underdeck bungie hold down system right now. The
: front hatch has warped and the edges stick up from the deck while the
: center is flush. How do I take the warp out of them? Heat? Straps? Should
: I go to something that will hold the edges better, like the Moby Latches?

: Charles Robinons