RE: M/T Hatch cover
I would use exterior grade plywood ( not marine $) and coat twice with slow set epoxy. Epoxy the strips down as well and use teak deck caulk for your seams, there are many brands. Do not use 5200 it's not for teak. Right before you fill the seams sand if possible the teak and then wipe good with acetone or denatured alcohol. The key to the caulking sticking is the removal of the oil in the teak.