Probably the propane/CO detector. Generally, they are wired in so the battery disconnect does not affect them. Also, the radio most likely always has a slight battery discharge going to it.
Most rigs will last a bit over a week without some type of battery charge. Best to do as you did - disconnect one of the wires from the battery or put a switch between the wire and the battery.
Barney
2004 Sunnybrook Titan 30FKS TT
Hensley "Arrow" 1400# hitch (Sold)
Not towing now.
Former tow vehicles were 2016 Ram 2500 CTD, 2002 Ford F250, 7.3 PSD, 1997 Ram 2500 5.9 gas engine