I am 90% sure this is your problem, OP.
I was having drain issues after I put in an AUX fusebox wired directly to the battery, even though the things running off of it had individual switches. I would suggest adding in a switchable breaker to turn that off when the truck is not in use.. or possibly an ignition relay for the fusebox.
Interesting. I have a bussmann breaker installed. I had this same set up before but was having the pre wires harness. Now it's all the same just everything in one spot.