I am currently in the Norfolk area, and there are several tunnels in this area, the issue is that the tunnels here are not going through a mountain, but going under water. The tunnel is there so that large ships can pass over the Highway, so this tunnel goes way down then has to come way up. The issue becomes that Propane is heavier than air, so in a tunnel of this type, if the propane would leak out while stuck in the tunnel then the tunnel could become filled with propane creating a disastrous situation (either asphyxiation or explosive). Thankfully in my experience there are plenty of warning signs about the tunnel coming up and even a pull off inspection place before entering most of these tunnels, and all that I have ever had to do was turn off my propane tank or bottles before proceeding through the tunnel. It there wasn't a pull off there is at least another exit after the warning signs.
My MH only has 1 40lb tank. I haven't done the perfect math but if a 20lb tank (BBQ size) is generally considered 5 gallons then I have about 10 gallons or about 38 liters
