Armored Harbor

I've been thinking building some sort of armored harbor for Huntington to park in when she's not needed and I think I may finally have a viable design.  This involves modifying a styrofoam cooler by cutting off one end and cutting a hole in the bottom.  Then I can toss this in the water upside down.  Hopefully it will float and might require some balasting to make it float level since one end was cut off.  Either way it would hopefully provide some protection from stray rounds damaging the club's rescue boat.  I hope to go shopping for foam ice chests in the next week to see what I can find and make some measurements on Huntington in an attempt to determine if this will even work.  Will suggested lightly attaching waterproof canvas to the exterior to enhance the level of protection.  I think designing an anchor system that allows the harbor to move will be a good idea as well.  This would allow some of the energy in the rounds to be converted to kinetic energy in the harbor.  I get the feeling that if I can come up with a good solution for this that this "Harbor" could have other uses including as a mobile practice target.