I´ve seen a number or bike trailers for hauling kayaks. You can haul a lot of stuff in a kayak.I´m not aware of specific regs.
but lawmakers always find a way to look busy by making laws that cost money or limit freedom..or both. I´ve built
a trailer for my inflatable kayak with an internal frame of 1¨ pvc pipe. Deflated it lays flat to reduce wind resistance,
kinda a 2 wheel travois.