In addition to the legality of double tows or not, there is another "law" on the books for every state regarding the total length of your RV rig.
Click here.Alabama:
Total length: 57 feet; trailer length: 28 feet 6 inches; motor home length: 45 feet; width: 8 feet 6 inches (excluding mirrors and safety equipment, and appurtenances up to 6 inches attached to a motor home, travel trailer, self-propelled camper or house car, truck camper, or RV); height: 13 feet 6 inches.
Although it is quite common to see RV rigs longer than your state requirements, as a resident of your state, you need to be in compliance with your state of registration.