For anyone who hasn't seen it, my main electronics bay is a piece of PVC pipe with arcylic end plates bolted on.
For waterproofing the cable entry points, I considered normal cable entry glands, but realied that the wire insulation alone wouldn't be squishy enough to keep the water out. The solution was: once the wires are through the glands, fill them up with silicon bath sealer.
Which would probably by fine at low pressure shallow depths. I want to make them a little more robust, so, once the silicone is cured, I withdraw the blob of slicone from the gland and tidy it up a little with a sharp knife.
This allows it to be re-inserted (saliva is an excellent lubricant for this!), but pushed slightly further back in, so it protrudes beyond the cable clamp. The cable clamp rubber grommet which comes with the gland can then but put over the already cured silicone.
This allows the clamp to compress the silicone, hopefully keeping it even more watertight.
Will it work? Who knows. Hasn't made it to the water yet!!
Oh, don't forget to "label" the wires before you mould them in the silicone. I did it by applying 0, 1 or 2 bands of heatshrink on either side of the gland.
Can't wait to get this in the bath and see if it works!