The kids really are working under there, not resting. They're marking the frames and stringers so we know where to place glue and clamping screws.
I've performed a few tests to determine deck stiffness, toughness, and weight of various deck combinations. I chose to compare 1/4" Okoume w/ one side laminated 10oz cloth, 3/8" Corecell a500 w/ topside 10oz underside 6oz, and 1/2" Corecell a500 w/ topside 10oz underside 6oz. The 3/8" thick sandwich weighed half that of the 1/4" Okoume and was approx the same stiffness. The 1/2" thick sandwich weighed 25% less then the 1/4" Okoume and was twice the stiffness. As far as toughness is concerned, I dropped a 3 1/2# round weight for 3 foot high onto the samples. The weight went right through the Okoume and bounced off the 1/2" foam core. It took several drops of the weight to show a significant damage to the foam. Cost and labor is significantly higher for the foam lay-up and installation and the areas where hardware mounts will need reinforcement. I plan to use the 1/2" foam combination on the deck and the remaining sheet of 3/8" foam on the cabin top.