The electronics of this design appear sound, but the first design failed at depth to keep the water out. So, on to design two.

A commenter suggested I look at converting a waterproof flashlight to contain the camera, and this seems like a fabulous idea. Waterproof flashlight are cheap on eBay, but there's always a questions of how "waterproof" they really are. Are some searching I found a $10 flashlight rated to 80ft on Amazon (https://smile.amazon.com/Flashlight-Flashlights-Submarine-Waterproof-Underwater/dp/B01K6K69R6).

The internals are easily removed; I just needed to get the cabling into it without ruining the waterproof seal.

I'm attempting to do this without potting or epoxy, so I chose to use a cheap cable gland. I drilled a hole in the base of the tube

And inserted the gland and wires

At this point it became obvious that this wiring was not going to work. In Design 1 I had water wicking between the wires and into the camera. This design would suffer the same problem. Time to change the wiring.

This time I used some cheap 4-core phone cable. This has an outer shield which would waterproof the internal wires and provide a single surface for the cable gland to grip. However, there was a mismatch between the diameter of the wire the size of the cable gland (an M12 - the smallest I had). To fix this I used some 1/4" marine heat shrink tubing to thicken the wire where it entered the gland.

And here's the final assembly

Visually the seal looks good.

Back in the 10ft water tube and the megohm meter showed a resistance >1000 MOhms. Now to leave it overnight and test tomorrow.