Fear not, old chap...plastic insulating tape is waterproof, providing you get it all level and there are no lifts on the edges. And this plastic insulating tape is council insulating tape, it sticks like superglue.
I used it on the previous camera on the previous Neptune without any problem whatsoever, and I always used it to secure the access hatch on my fast electrics(back in my youth, you understand...before the force overtook me)
I thought of everything to secure the camera to the hull...rubber bands, velcro, blu-tak, then came up with my present system. We'll see how good it is tomorrow at Alfold Show...