Just looked at my old posts and it turns out i got my L5 in December 2010 .
So just gone 7 year without so much as a BOOM 
Who'd a thought?!!! Last thing i remember about all the old posts was guys who can't wire a red and black together and fit a pump, seeming perplexed when it didn't pump water telling us all we'll be gassed to death if we have them in our vans !!!
I do think that there is more to it than meets the eye , i mean with regard to using a little bit of savvie so to speak , dont rush the install , use high temp water hose , think about where to site the boiler very carfully , dont put the gas supply hose under any stress with regard to tight bends , vent it all very well .
At the end of the day what can go wrong , bottles very rarely fail , if gas does escape and you have vented properly you should not have an issue , if you cant smell propane then you should not use it ( bloody stinks ) , always switch off the boiler and turn off the gas , even if the next stop is just down the road , just common sense .
The only time you could have a problem is if you spring a leak whilst in use , it may well happen but again if vented well enough it should not be a massive problem .
I think maybe a look at flash arresters as used by oxy/acetelyne users is an avenue to explore , maybe in conjunction with that gasstop thing .