Ed,
I've known I was cheap for a long time. It seems to me that a tire designed to last up to 50 miles at a time (they don't tell you to discard it after 50 miles) with a few thousand miles on it should do nicely on a boat trailer with a few hundred pounds on it. It would be a larger diameter than the 12" trailer tire currently on it. Actually it looks like cost wise trailer tires are probably cheaper.