Hey Rehd,

I apologize that this isn't an answer to your question - but...
I bought ready-made bags for my baidarka-ish boat that I find very appealing. I bought them from Corey Freedman of SpiritLine kayaks ((360) 299-0804 http://www.skinboats.com/page2.html) up in Anacortes, Wa. Each airbag consists of two identical airbags connected one on top of the other. The middle forms a dry bag with the familiar rollup top. The amount of storage is modified by the amount of air in the bag(s). Mostly I keep them fully inflated - but if I need to bring some stuff - deflate a bit - put stuff in - reinflate. They fit my 16.5' x 22.5" SOF craft. I can measure them if you are interested. I don't remember what he charged me - but it was very reasonable and it was like doing business in the good old days. Call up and talk to Corey personally - he takes my order and ships the bags. On receipt - I sent him a check. I hope nobody rips him off - because he will probably close up shop rather than come into the new millienia. Great product - great guy. Apparently he runs a pretty cool boat building school too.

Cheers,
PC