Question 1 - Get an Extend-A-Stay kit
. It will let you attach a portable LP tank. The only catch is you will need to find a safe place to carry the tank if you intend to take it with you. You can also usually rent larger tanks from the LP dealer.
Also, by buying an additional hose, you can turn the Extend-A-Stay into an Extend-A-Flow, which lets you attach a propane grill to your motorhome LP tank.
Question 2- I don't know specifiaclly about the Baltimore Tunnel, but most times "No Hazmat" means no bulk
transport of hazmat. We crossed one bridge (can't remember where it was) where they made us pull over and shut off the tank valve. However, it's best to chack in advance if you know there will be a tunnel.