Something I thought of..... but I am not at that point yet.......
Hot glue. I know hot glue is a little brittle...and I am not sure of it's properties with regard to conductivity.....but it was just a thought. Perhaps drill a small hole or two... for the glue to "squish" up through.... before it sets.
I have used silicon sealer for this sort of thing before. Although I see a lot of people stick the PCB's to the underside of pots with those little doule sided sticky white pads. They seem to last forever, and are a devil to unstick from anything smooth.
