For the past two weeks, I’ve been having trouble with some of the 12 v system when disconnected from shore power. No lites, water pump, fans or power cord reel. Connecting truck cord doesn’t help. Initially when I disconnect, the 12v power will cycle on & off for a few minutes and then off. I get power to the slides, jacks and residential fridge thank goodness! If I start the generator I get all 12v power back. The biggest issue is the cord reel as I have to reel it in by hand or start the generator. Battery voltage is 13.3 but drops to 12 after a travel day.
Any suggestions would be greatly appreciated.

Check the Battery Disconnect switch in the Battery Compartment. If it's in the wrong position or has failed you won't get any 12V without shore or generator power. Also it won't allow any charge voltage from the TV get to the batteries.
I had a 12V issue on our '12 36RL and found the nut on one of the terminals of the disconnect switch about ready to fall off. Tightened same and problem solved.
When disconnected from shore power, rotate that switch while someone monitors lights and see if you get anything.