A schedule 40 PVC 2"x2" T piece with a threaded 1/2" exit works great for the keel, leading edge or Xbar.
Or a 3/4" x 3/4" x 1/2" T for sprogs and downtubes.
Cut off a bit more than half.
Also take off the sharp edges and bevel the corners (while you fill you hair with white PVC crumbs)
Mouse mat neoprene works great and seems to last for ever. Well 4 years of Tandems and counting.
Shoe Goo works a treat for the bonding (don't sniffit - its not the good kind of glue)
SLIK SBH 60