Minicell is relatively heavy and expensive, isn't it? Should work good though.

But the OP doesn't seem to care, I think.

Doesn't care about what? With respect, the original premise I was arguing against was "if a hatch cover fails your boat will sink like a stone, but if you do anything whatsoever to provide avoid this, you're just being a worrywort."

It turns out the person who said that without bulkheads a strip kayak would sink was incorrect. So my initial point, that a boat should have sufficient flotation such that it won't sink even if completely swamped, has already been satisfied.

Beyond that, certain posters seem to be saying that they believe that in the event of a hull breach their boat is going to sink and they're perfectly OK with that - but most posters have said they do, in fact, use some form of flotation, but they have pointed out certain problems with the typical forms of flotation - the bags sometimes leak, or they take up a lot of space, etc. So that's where the discussion of how to custom-fit flotation into a boat hull came about.

So I'm not sure of what your point is here exactly. Is it that you already have a form of supplemental flotation that you find works perfectly for your needs and has none of the drawbacks others have mentioned? If so, what is it? Or is it that you use flotation, you acknowledge it has issues, but you prefer flawed solutions even if better ones are possible? Or do you think this whole "flotation" thing is just nonsense, and a real sailor knows that in the event of an emergency, the best thing is to just drown quickly and get it over with? :-)