This is a cheeky little phase in construction because it calls upon a material which is strong in compression and also in shear, in the form of a low-density insulation foam. The benefit of this is that it is available off-the-shelf, albeit rarely intended at your local DIY store for flying machines.
One way of cutting this to suit is simply to place it about where it's going to be and just knick the edges with a Stanley knife before using the same tool and a yard-stick to eventually cut the panel to size.
Then flip the frame over (note the right-pronged appearance) and apply a silicone seal around the edges before squeezing the foam into place. When you do this, spread the weight gently and evenly so as not to crack the foam within its foil-backing.
You can see that we are good to go from the last picture, whereupon we rivet the next sheet-alloy square to form a cap on the underside.
