Typically states will abide by the motor vehicle laws of the state you are registered in. There are exceptions to this, where you have to comply with the state you are travelling in. Two examples come to mind, in Arizona where I live, it is not required for a motorcyclist to where a helmet, but travel into California where there is a helmet law you better have one on. Also, more specific to this forum, again in AZ you are allowed to double tow up to a certain total footage without a CDL, but some states require a CDL. When travelling to such a state, you would not be permitted to drive on their roads without a CDL. In the case of the tow dolly, it seems at least most states do not require registration, so I would guess that if there are any states requiring registration, it might defer to the state you are licensed in. It would be worth your while to certainly check your own states requirements, but also check any state you will travel in to be sure.
