Hi all ; I'm building a 16' stitch and glue canoe . The plans I'm following show the floatation compartments being airtight sealed by a bulkhead and the deck. A fine idea if you can be sure it's 100% waterproof. I'm not sure my building skills can garauntee that. Would floatation foam give a similiar amount of displacement? I've never used it before , how does it work and how much would I need? Thanks...Jeff