If it has bolt on hubs I have seen places just space the top two to get the camber back in. Normally I would think that it would have to be pretty bad on a boat trailer (over -2) to see a large amount of wear. I would string it to check for a toe condition in this case and it could be a combo of the two. Out of toe will tear the edges of a tire off much faster than camber. Just my two cents.