These are pieces of Divinycell H80 that is 1/2" thick that I've cut to size to core the top cap.
I used Dura Bond Epoxy to bed the coring pieces. After mixing it up I used a notched trowel to spread and groove it.
After the coring set up I used a razor knife to bevel both edges of the Divinycell and glassed it over with a 1 1/2 oz matt.
Jumped back over to the face of my rear compartment and cut the access panel locations. On each side will be a 12" x 16" hatch with removable lid and the center will be a 20" x 14" hatch that will be hinged and swing to the left.