Here's another data point for you.
I was out in the camper last night with 2 inside lights and the porch light on. I have my battery on a timer to where it only charges 30 minutes twice a day at 10am and 10pm. It isolates the battery from the camper so the lights were being powered 100% by the converter.
All was quiet while I was working for about 20 minutes and all of the sudden the converter fan kicks on. I looked at my watch and sure enough it was 10:02. The charger turned on. I turned off all the lights and the fan stopped. I turned on one light and the fan came back on.
I still think you need to do some battery maintenance.