I suggest checking out the link I posted. It is for non-commercial vehicles, and the way I read it, no matter the size of the tanks, only two max are permitted, and they would be limited to 45lbs each. That size of tank is bigger than most RVs, but a lot of RVs now have the design to carry three tanks, which would not be permitted:
compressed-gas(For Non-Commercial Vehicles)
Maximum capacity: (a) Not more than two non-permanently mounted containers having maximum individual capacity of 105 pounds water capacity or 45 pounds LP-Gas each, or one container having maximum capacity of 60 pounds LP-Gas, or (b) not more than two permanently mounted containers having maximum total capacity of 200 gallons water capacity LP-Gas when used as a motor fuel. Tanks must meet the approved standards of the Department of Transportation and are subject to inspection at toll plaza. They must be properly secured and valves closed while crossing the facility.