Re: remote/auto control for propane tank?
Having your belly bin un-vented might create a potentially dangerous situation. I would make some kind of escape vent. One possibility is to remove part of the floor under the tank and install expanded metal. Or put louvers in the door or the back wall.
Failing that, paying $445* may be a small price to pay, if it helps you sleep at night without worry. If I were putting that system in your bus, I would install the included remote sensor in the belly bin wall lower than the tank, *plus purchase another sensor to install near the floor inside. The automated system promises to shut off the low-pressure supply (after the main pressure regulator) if any of three sensors triggers.
If one were interested only in the remote turn-off ability, and can install switches and wiring, the actual solenoid valve without the automated leak detector control system is only $106. As an alternative, propane standby generators have solenoid valves that open during "call for start/run" conditions. It may be possible to get one from a generator dealer, or even salvage a working one from a generator being scrapped, if you have the right connections.
The solenoids used in generators require a continuous flow of DC to an electro-magnet valve to keep the gas flowing. When the generator is running and charging the battery, that isn't an issue. If you are boondocking and running down your battery bank to keep the gas valve on, it is an issue. Yachtsmen are often more conscious of power use than boondockers, so the automated system may actually employ a motor-driven manual valve. Momentary application of power might turn the gas on, and another momentary application turn it off. This would be more acceptable in terms of power use. The sensors and the "brains" of the automatic system will require some constant power, though.
Remember, if any of your LP appliances have a pilot, turning the gas off and back on without thinking may cause gas to flow unburned through the pilot jets. Having a remote switch makes those mistakes easier. if you had no gas refrigerator, but only had a stove that used no pilots (spark or match light), and if any LP water heater or furnace had electronic ignition, it would be OK to install a manual remote switch without concern.
I would think that the only non-emergency use would be to turn the whole system off for travel, going through tunnels and other controlled areas. If a leak was sensed without the automated brain, it would be handy to have a remote switch to shut down the system without running outside. But I would not want to be throwing manual electrical switches in an enclosed space during a gas leak, possibly causing a spark. I would go outside and close a manual valve. A ball valve installed at the tank, where a quick 90° swing of the lever is all it takes to kill the gas flow not too hard to operate. The handle position also serves as positive indication of whether the gas is on or off.
For my designs, I would not want to be running down my batteries with a valve, nor would I like to spend that much. I would have my tank(s) either under the bus, or in an outside cabinet with no floor by a back door if I were to build a porch or similar mod. I would have ball valves, one for the system plus one for each tank if installing a manifold set-up. As a side note, we have no propane detectors in our home, and found that more than once at least one of the cats has climbed onto the cookstove and cracked the valve for a burner on a little bit. The first time it happened, it took a couple of days before I figured out what the odd smell was, because in the house the propane scent didn't seem normal. Propane needs to be taken seriously, but not fearfully.
Someone said "Making good decisions comes from experience, experience comes from bad decisions." I say there are three kinds of people: those who learn from their mistakes, those who learn from the mistakes of others, and those who never learn.