Tidy LPG filler cap setup

My only concern would be the stress on the bodywork from the heavy filler/pipe.

On my Saab and Volvos which I had the conversion done I had the filler fitted to a bracket welded to the tow bar. that way you don't need to cut/drill the bodywork, its central to the car so you don't need to care which side of the pump you pull up and its 'out of sight' unless you really look for it.