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I run a few different boats and one of them has an open cockpit with no benches or other seating- a roto molded cooler or even a flat top igloo works for seating. You can mount tie downs for it or keep it loose depending on size and hp/speed of boat. If you really want to limit the footprint in the boat- a 5 gal bucket with a hunting/ice fishing seat on it works great as a mobile seat and a storage container.
