I'll throw my opinion in.....there's nothing wrong with a shared chamber. I've built hundreds of boxes that way, and i don't think it's ever been an issue once. Built right they're not going to flex, so that's no concern. Blowing one sub and eating up the other is potentially true, but when even some of the less intelligent people I've dealt with blow a sub they seem to notice it. Always utilize proper system design and people won't often blow subs anyhow.