Unless you have a high wall model PUP, the fridge does not use DC when on propane. There is no 12V "control board".
Once you have LED lights inside, the biggest user of the battery is the heater fan. With a single decent, fully charged battery, the heater can run for about 8 hours (actual run time) before the battery reaches 50% and needs recharging. I am assuming you are not running the stereo or other fans, in this calculation.
A dual 6V golf cart battery setup gets me 4 nights of moderate heater usage in my A-frame before I need to recharge. Leaving the water heater off except when needed (we rarely use the water heater when camping because we wash dishes at the picnic table using water heated on the stove) does save a little on the battery.
In the summer, we use the Fantastic Fan on low to circulate air, and not the heater. This draws about half of what the heater fan does, so it works out to the same 4 nights without recharging.
I did install a battery cut-off switch that turns EVERYTHING off. Then I don't have to fuss with disconnecting a wire - strictly a convenience. However, the battery needs to be reconnected while towing to power the brakes in case the trailer becomes disconnected. See photo below of my disconnect switch mounted on the battery box.
just our experiences
2014 Rockwood A122 A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time