H'mm are you sure it is not the smoke alarm chirping? Most LP detectors are powered off the 12-volt coach battery and if you unhooked it, and on top of that pulled the fuse, it should shut up if it is the LP detector.
It is common that cold weather will drain a dry cell battery. I have had many times a smoke detector go into low battery after sitting out in the cold. Many brands go into chirp mode, as a last dying breath when the battery goes low to tell you it soon will no longer be working.
As far as turning off the LP gas at the tank, I turn the LP off any time I am not using the camper. If there is ever a very fine leak like in a gas valve, (can be common) it will drain your tank. In addition, if the leak is large enough it can present a bigger problem. I could not tell from your note if you had left the camper or was using it.
Unless some one modified your camper, or your have a real special, unplugging from the AC power and unhooking the battery should kill any power to devices that Sunline wired in place. The smoke detectors are dry cell battery powered and if anyone added an extra carbon monoxide alarm, they too are dry cell battery powered and have chirp mode.
Good luck, hope this helps, and for sure let us know how you make out.
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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