Below are pictures of my cedarstrip floatation-wanigan made from leftovers from building the canoe. I slightly trimmed down the forms used to make the canoe so the wanigan fits perfectly in the bow or stern. I cut off about the last six inches toward the stem and flattened it because it was wasted space (too narrow for storage so unnecessary weight).
I've only used it once as a wanigan and that was when I had no portages to do. I've never gotten around to installing handles and probably never will. But eventually I'll rig up a tump line for it.
I have used it a couple of times for floatation when playing around in whitewater. It has worked well and only a few drops of water ever got past the rubber seals and that was probably from opening it wet to see how dry it was. It gets tied in with the use of two small brass eye hooks screwed and epoxied into the inner stem of the canoe. It fits snug so there isn't much stress on the eye hooks.
Sorry, no pictures of it in service.