In Virginia the tunnels has signs and the general thing to do for RV's is to turn off the PROPANE valves. This may only apply to tunnels that go down a long way where Propane can accumulate I guess... They will inspect to see if the PROPANE is turned OFF and tanks are secured to the frame...
Chesapeake Bay Bridge/Tunnel here in Virginia is the only one I have pulled a trailer through with Propane Tanks and was checked at a very well marked pull-off just before going down into the tunnel.
This is brief summary found on Google about the subjuct...
PROPANE TANKS IN TUNNELS for RV'sCheck ahead if you know your route. I think in MD some tunnels in the Baltimore Area on I95 may be prohibited for RV's with propane tanks and you have to route around them... Was that way just a few years back at any rate... The report above may have some info on this - I didn't read it haha...
Roy Ken