While the camper us upside down for bottom finishing/painting I am using gravity in my favor. I’ve glued the spacers together (with the wire channel between them) and plan on applying epoxy/cellofil glue to them and setting them on the hatch top with a lead weight or two. Caution will be taken to insure that the wire channel ends up in the appropriate forward corner such that the hatch hinge installs forward, not aft. Then after I right the camper and set it on the trailer I’ll drill corner holes from the inside then saber saw the hatch cutout from the outside. I also used 3″tape on the bezel to roof inside seams, rather than a whole square of 6 oz cloth as depicted in the hymnal. Less glass and epoxy, same basic result. Also while upside down, I am gluing in 1/2″ thick circular mounting pads for my cabin dome lights.