It's not that a double O-ring can't work, just not where they're both competing for clamping pressure at the same time. My theory is that if you take a 70 durometer O-ring (hardness) and double it up, it's almost like a single 140 durometer O-ring. You have to clamp twice as hard to get the same seal. It gets even worse if the inner one touches first (no matter how slight). If you can get a second O-ring machined into the housing body itself so that it slightly protrudes the outer circumference of the body and seals against the inside wall of the coupling, that would not compete at all with the primary o-ring. Here's the thing, many of use used a single O-ring design with no problems at all but the one person that tried double rings had a leak.
The O-ring should have no tendancy to extrude. It should sit pretty tight around the outside wall of the housing body. Outside water pressure will push in on it, not pull out. I don't think putting a bevel on it would necessarily hurt anything as long as you can machine it perfectly. I'm not sure there is any real benefit though.
My cam is right up against the front window and there is a plastic lip around the whole thing that hits before the lense glass. It barely touches if at all. If it's too far away though, you can have light coming in from the rear window and reflecting back at the lense.
Good luck.
Bobby
