In the electronics world that black stuff is referred to as potting compound. Any two part epoxy or even ester based resin will probably be fine. Most fiberglass things are done with ester resin because it's cheaper, carbon fiber and kevlar with epoxy resins because they attach to the fibers better. Mix it VERY well (and for a couple minutes longer than you think is needed). Also, ester resins tend to put off a lot of fumes, and pretty much all resins don't come off once you get them on something, so don't use them inside.
Most resins will cloud if you cure them in a moist environment, but once cured they're pretty much inert.