hi paul sounds like you are having all the fun
have you tested the battery as well as a parasitic draw test you could also check the body control system for faults that may be caused by modules not shutting down.
does it have vac cdl if so they have been known to give problems as well as water ingress into front fusebox/lim unit
but the first step is to see if there is a drain on the system and how much is being drawn
hth martin