You don't need fancy float bags -- or even waterproof ones.

Use floataion pillows. use old pillowcases, or just make a few stuff sacks from scrap canvas and fill them with the foam packing peanuts that seem to come with everything. Or, chop up chunks of the foam packaging materials that come with appliances, and put them in your bags. The bigger the chunks the better, as long as they fit in the bag, and the bag still fits in the boat. You can puncture these things, and they still float. if the foam gets grungy over a period of time, trash it and refill the bag. If the bag gets grungy, dump out the foam and throw the bags in a washing machine - or stitch up a new one.

Just be sure you are not using the watersoluble packing materials.

Nothing like recycling to give you some free. flotation.

and for anyone thinking of using expanding foam -- mix in chunks of pakaging foam and your expanding foam will go further. It should suround and secure the recycled plastic, filling more space for the dollar.

Hope this helps

PGJ