Suds
The L5 is very easy to fit. You just fit it inline after your pump and before the hosereel and connect it to a gas bottle!
Don't need a plumber.
I looked into it but felt safer going for a diesel heater and have just booked in with Pure Freedom.
There is more info on the ACS forum in the hot section. I think the only extra bit you need to buy is the gas regulator which is the pipe and control which connects the L5 to the gas bottle as the one that comes with it from the US is a different spec.