An internal tank probably has an electric shutoff solenoid in the circuit. It's run off of the propane detector and is a safety feature that shuts off the propane when the detector goes into an "alarm" state. The coil in the solenoid on my 2011 Georgetown 327DS shorted and blew the fuse protecting the propane detector. Of course, the fuse wasn't in the fuse panel. The propane detector is fed directly off of the house battery's + terminal and has its own 5A inline fuse in the battery compartment. (Yes, locating that fuse was an interesting chore.)
I discovered that the solenoid is NOT a replaceable part! The only way to get one is to purchase an entire new propane detector kit which includes the solenoid. Unfortunately, the new solenoid had different sized fittings than the original. Fortunately, the RV mobile technician who was installing it at the campground I was staying at brought a full set of adapters and had one that fit. My breakdown insurance also covered the entire cost of the repair, over $700.
I also discovered that the original solenoid was rated to draw 1A at 12V. This means that having the propane turned on was drawing 24AH/day from the house batteries. The replacement solenoid is rated at 0.5AH, requiring only 12AH/day, a desirable improvement. Since my rig was only one year old when this happened, I still had four years life left on the original propane detector. The new one that came with the kit has been put in storage (it has a 10 year shelf life) and will be installed at the end of the original one's service life.
I also took the service technician's recommendation and installed a switch in the power line between the propane detector and the solenoid. This lets me, when I don't need it, shut off the propane from inside the RV.