Has anyone installed one of these as a little forward day hatch? Seems like cutting the deck could be high drama...

I have a plastic fishing SUP that came with one of these access hatches. I sometimes find that pooled rainwater has made it through the hatch seal. I'd test the seal on yours prior to cutting into your deck.

Assuming the hatch fittings are flat, how would one compensate for the curvature of the deck?

 

Why would you need this? You are just asking for headaches. ))