David is the flame in the heater isolated? The air vents that cause it to blow out shows its not contained, or is it? Obviously i think the gas box is a great way to go. I'll have to look further into that.
Yes.
If you look at those pictures of my set-up you'll see the heater is separated from the gas bottle by way of a solid stainless steel panel (heater is by side door, gas bottle is in the rear).
If the pilot light goes out, the gas automatically stops flowing to the heater. You will have a tiny amount of gas escaping from the pilot light but you're drop vent and ventilation (no van is air tight!) will remove this tiny build up with ease.
If the pilot light goes out, you have just removed the source of ignition - gas cannot ignite without a the flame - 'Fire Triangle'
If you are isolating the gas supply between each job (turning the gas off at the bottle) and you're doing your Daily Visual Inspections and User Checks you would notice if the gas bottle itself was leaking gas before turning the system on.
These Daily Checks and User Checks apply to ANY system and not just gas systems...but I'm sure we all know that