Good thinking dazmond, am not sure how long the barrells will last tho,  thing is, it could be mot, clutch or any problem and how many of us have a back up set up if van was to be off rd for a week. 
I have a trolley set up which I lend out to a friend so worse case scenario. 
Am also in the process or doing a pallet set up,  basically I have a pallet with a 300L tank, I already have spare hose and reel so am going to pick up an 11L DI bottle a pump and controller and hey presto. I can then drop this off at sites and use a pump truck trolley to shift it about.