"alarm 1" on panel, going off in basement

[Sbolles4]

We have a 2013 36RL. It is for sale, and still winterized from last fall.

We have an alarm of some sort going off in the basement, and draining the battery. On the control panel, it shows as "alarm 1". My husband has tried to trace where it is, and can't seem to find it. As the RV is winterized, we're thinking it shouldn't be a water alarm. The CO detector isn't going off in the living area. Could it be a propane alarm? Or an alarm of some other sort? I've been searching layouts and manuals and haven't come up with much in the way of explanations of alarms.

Any ideas are appreciated (including hints on how to locate the alarm in the basement!).

Thanks,
Don & Sharon