Check the condition of your battery. Maybe erratic voltage spikes (like
trying to charge a dead cell?) are triggering the alarm.

I know of many solid-state electronics devices that start acting wonky when
their power source goes unstable.

Just an idea...
-Dave

This group is specific to AFrames and I know this subject has been
discussed many times, and solutions offered.
http://autos.groups.yahoo.com/group/alinerchaleta-frames/

--

The gas the battery gives off would not trigger the propane detector
(although some other gases similar in structure to propane might).
Carbon monoxide will also set off some propane detectors but only at
alarmingly high levels (no pun intended).

Since the detector still sounded the alarm with the gas cylinder hose
disconnected, it is unlikely that you really have a propane leak.
Rather there is likely something wrong with the detector.  Vermin
chewing the wires would disable it, not make it sound continuously.

The sensor in the detector is probably corroded or bad, or there is a
short in the electronics.  If it is still under warranty (and it might
be from either the propane detector maker or the camper manufacturer),
you should return it for a replacement.  If it is not under warranty,
you should replace it yourself...they start around $50...well worth the
safety for you and your family.

Disconnect the battery when parked unless you are supplying 120V to
the converter.

The propane detector *will* draw down the battery, and the alarm is
*designed* to go off if it does not have enough 12V power to do it's
job.

Austin