Actually sometimes you mold a part, like the stereo on my first post. Sometimes you just purchase a "potting box" put your stuff in that and pour the resin in on top of it. Potting boxes are really popular in the automotive world.
And yes, once they are potted, there' in there for good. Rework is not going to happen.
Now for doing LED things? Clear Urethane is the ticket.
Builders of marine Stereos, LED lights, Sailboats and whatever else looks fun.