[url=http:/www.walmart.com/catalog/product.gsp?product_id=3560021&cat=134922&type=5&dept=4171&path=0%3A4171%3A14521%3A117932%3A134922/]Walmart Bumper Boat[/url]
Saw one of these @ my local Walmart, interesting...
Kind of pricey for a 12v motor, and I don't know how big it is; but it's probably in a water tight enclosure, and maybe has an impeller/pump jet.
Maybe they will be on sale at the end of the summer season. It would be fun to take one apart and see what could be used for a sub.