This is the point where I want to take some of the weight out of the module itself. The deck and frame are made of sturdy 1/2 inch cabinet grade plywood and because I plan to place foam insulation board over most of the surface, I can remove some of the deck where it will be covered.
In case you were wondering what a hole saw is, it is a round device that fits into an electric drill motor with saw teeth along the leading edge that cut a nice circular hole. There is a 1/4 inch drill that guides the alignment of the larger saw blade. After cutting about halfway through on one side, I switched to the reverse side to finish the hole. The drill bit will have made a hole all the way through that will insure the cuts on each side will line up.
Because of the density of this wood those disks represent about 3 pounds.