Both house and chassis batteries are in the battery compartment and each has a disconnect switch. Are there any wires whatsoever terminating on the battery positive posts or the battery side of the disconnect switches? It seems there must be some parasitic or spurious device or load drawing current from the batteries. Assuming there is just one such device or circuit, it seems the two batteries must still be tied together through some path, perhaps the device that prevents discharged house batteries from taking the chassis battery down and leaving you stranded.
Personally, I'd want to know what the causes is. However, if the perpetrator cannot be found, it might be time for a trickle charger (battery maintainer). Or maybe one for each battery.
2020 GMC Denali 2500HD Crew 4X4 Gas 6.6L
2015 30' 8280WS Rockwood Ultra Lite - lifted 3"
Solar plus LiFePO4 and 12V fridge.