[JohnB]

I am not sure I would put the foam back in. I would drill some drains near the bottoms of the stringers, and then use epoxy to stitch and strenghin it. Someone else might want to chime in, but I don't think the foam in these was structural, but I could be wrong. The foam just created a convienant mold to make the boxes. The glass box of the stringer is it's strength, and epoxy will give you a lighter stronger material and a chemical bond in addition to the mechanical bond.