This is what their website says: "Code of Maryland Regulations (COMAR) govern the transport of hazardous materials across our toll facilities. Under these regulations, vehicles carrying bottled propane gas in excess of 10 pounds per container (maximum of 10 containers), bulk gasoline, explosives, significant amounts of radioactive materials, and other hazardous materials are prohibited from using the Fort McHenry Tunnel (I-95) or the Baltimore Harbor Tunnel (I-895). The Francis Scott Key Bridge (I-695, the Baltimore Beltway) is a convenient alternative route for crossing Baltimore's Harbor."
Sounds a little archaic to me. I don't think many Rvs are sold today with only 10 gallon tanks. I have not towed through this tunnel, but have contacted other tunnels where I was towing and was told that my tanks ( two 30 pounders ) were ok, but they preferred to have the gas shut off while traveling through.
I would contact them directly to be sure. Here is the MDTA bridge police contact info: Tunnel Command
Fort McHenry Tunnel (I-95 from Caton Avenue to northern Baltimore City line) and Baltimore Harbor Tunnel (I-895)
Commander: Capt. Richard Ricko
Hope this helps,
Don and Michele
3 Adult Children - 2 Granddaughters
Present campsite - future homesite