How is about truck stops? All big truck stops have certified scale (I think with 10 lbs precision, It can be verified at fuel desk). Drive in with boat on trailer, get a weight, park at lot, get a boat out of trailer and weight truck and empty trailer one more time. For total cost of 7 bucks (6-first time and 1 for second) one can get a boat weight up to 10 lbs accuratcy.
Just a wild idea:-) - I used to be a truck driver
