We've had some pretty good discussions on this on a sailing list I belong to. If a vessel is documented it falls under Federal jurisdiction, and if it has a bed, galley and seperate head it is also a "second residence" in the tax codes, and could be argued as such as it has been so recognized by a Federal Agency.
I spend about 60 nights a year aboard our boat. If someone breaks in while I'm there and does anything but "drop" when I ask him nicely he's going to get a copper-jacketed angioplasty.
It's one of those cases, like a distress call from an unlicensed E.P.I.R.B., where if it becomes necessary I'll pay the fine as long as me and mine survive.
It was also suggested that if you need to deploy a gun you're not supposed to have, you might also be better off investing a spare anchor-chain in placing the second-place winner 700 ft deep in the lake or ocean and keeping your mouth shut.