A large diameter float noodle will keep a person afloat, how much does your trap weigh? I wouldn't put the floats on the bottom, secure them to the top or midway so it won't drag on the bottom too much when your pulling it in. Try a couple of empty milk jugs, I think you'll be surprised and it might be more flotation than you need. Larger zip ties with a large noodle going around the cage will still look neat. I think there's pictures of some fish cages on here that use flotation in this manner.

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