This gets worse the more I look in to it. I posted the same thing over at diesel stop in the trailer/hauling section and they came to the same conclusion that they rearly ever see brakes on boat trailers(because they dont last) but they were split on wether you had to obey the laws of the state you were passing through or all you need to do was meet the rules of the state you were licenced in, then you were ok. They had a good link to a boat us link here it is
http://www.boatus.com/trailerclub/laws.asp seems if I was leagal in Mass and my plate was good then I'm good to go, If I reregistered in a differant state then I would need to meet there standards. Heres on to think about , Mass has NO emmisions testing on diesels under 10000lb. GVW, If RI tests all of them do I go and get a RI emmisions test if I drive through the state?? No because I'm regeistered in Mass and meet there rules. I'm hoping that this applies to the trailer rules otherwise its a nightmare to meet any or all of the states rules????