I've heard of several who added fabric bulkheads to a skin on frame - here's a good photo documentary:

http://www.paavia.dk/Bulkhead.htm

Other ideas are carving big blocks of some type of lightweight foam to fit the bow and stern (you might be able to find enough styrofoam to glue up a couple of big blocks, or glue up blocks out of styrene wall insulation), using beach balls as float bags, and filling plastic bags with styrofoam packing peanuts. Then there's the sea sock, but that alone doesn't provide reserve bouyancy on its own.

Anything that's light weight and displaces water will work ok, but you really can't beat fitted float bags for their ability to displace a large quanitity of water.

No matter what you use, you'll want to take it out after paddling to promote faster/complete drying. Float bags make this easier than any solid float aid, just deflate and pull out. Putting them back in isn't as hard as it may sound, inflate them enough so that they hold their shape more or less, but can still be deformed to fit through the cockpit. Some add a simple pulley system, so that float bags can be attached to a light line and pulled into the ends (or out) with ease. That might not be something that can be implemented if you have already skinned (we are talking about a skin boat, right?).

: When I finish building my 18+ foot Greenland kayak (appropriate for my size),
: I'll want to put flotation at both ends. Since the only access point into
: the boat is the cockpit, and its a long reach to the bow and stern, I'm
: looking for an alternative to commercial float bags that will be annoying
: to put in and take out.

: I'd like something a bit more permanent that I can push in and leave, without
: worrying about deflation... closed cell foam comes to mind, but I don't
: know if that will work, and it can be expensive.

: And bulkheads just don't seem appropriate or workable.

: Anyone have any ideas? Thanks!

: cjk