I've used JB weld to try to fix holes in my old boat. It's an OK product, a little hard to work with, but I don't think it would work well for glueing something to your boat that would come under a lot of pressure.

Was he saying to put it around the bolts when you tighten them down or something? I could see doing that if you wanted the connection to be extra strong. If at all possible, I would bolt your holders and anchor pulley bases down with four 1/4" bolts.