Get a meter that can read in milliamps.

With the truck off - put the meter in series with the battery.

There will be current draw probably high at first.
Let the meter settle to a consistant current draw.

First check all the add on BS you have on the truck - radios and all the after market stuff that is not on a fuse.

2nd - pull out fuses - one by one and see if the current draw drops.
and
3rd - an alternator with leaky diodes can also draw current.

 

Thanks again guys. Got a meter and started doing my homework on how to use it, esp for testing parasitic draw like this. Will do, maybe this wknd. Found moisture near BCU? Down by the pass side footwell. May also pull that box and have a look. Also need to reseal sunroofs and water ingress points.