My HDX actually has a switch in the fuse panel on the bottom, in the middle, that looks like a toggle switch that opens and closes the door. I wouldn't imagine it would be a hard thing to accomplish yourself, just tie a switch into the back of the switch that's already there.
This is great for securing the door when you leave the bus as you can lock all emergency exits, then hit the switch and your main doors close, basically locking them in place with air; close the fuse panel, lock it there, and nobody is getting into the bus without forced entry (or the knowledge of the air supply lines like Rhombus pointed out above)
If you want, I can try and trace the wires on my switch to see where you could place one yourself.
The adventures of two full-time travelers from the Natural State, living in a bus and exploring life, one road at a time.
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