I subscribe to the caravanning & motorcaravanning newsgroups as well as this one; the caravanning group especially is plagued with trolls and crossposters.
Without getting onto the subject of why some idiots do this, how do you keep them away from here? Is it because there are a lot of muscular mechanic types here as opposed to the genteel caravanning folks or have you some more sophisticated electronic strategy [ such as Conor -:) ]
Kilfile isn't very effective as they keep reinventing themselves.