Screw the Law!! I would not ever think of brakes on a boat!! Any time I have had them they no work in short order! Ma. requires them after a weight and I have ripped them out and threw away first sign of trouble!
One more headache you don't need!!
I tow a 23' Sea Ox now, (about 6000# loaded ) and just bought a used trailer for it, tore the brakes out and put all new hubs on it. Tows great, and no breaks. Just slow down and watch the other drivers.