After glass layup two lite ply doublers were added while the parts were still curing and weighted to get a good bond. The parts were trimmed flush to the molds and the molds were fitted together.
I poured an amount of 2 part polyurethane foam mixture in the back of the part added the bulkhead with vent hole as shown, mated the two mold halves and clamped it up with c clamps around the edge. The urethane foam expanded to fill the boom and excess vented out the hole in the bulkhead.
These parts were extremely strong and light and a lot easier than building up booms from balsa.