Bongo Fury

Hi guys, sorry if this has been covered before, can't find anything on it, we got our bongo a month ago, absolutely love it!! Now to be on the safe side we got a co alarm, brand new fireangle, it went off that evening on the driveway so i assumed it was faulty so took it back, swapped it (b&q) and put in new one, 3 weeks later the other one went off again in the evening on the driveway! Nothing burning, gas turned off, brand new leisure battery (it's outside under bonnet anyway) everything turned off!! Im baffled. Anyone have similar experience?? I'll get another with display this time.

Was it a particularly cold night - not sure where you are, but that can be a cause?
Could someone else have had a BBQ/Bonfire and maybe left the ashes around (especially if damp) which might cause CO to enter the van from outside ?
Is it wired for power from the LB, in which case when was the LB last charged ?

It wasn't a cold night, I'm on south east coast, was around 15oC. Leisure battery is brand new last week and charges via split charger and solar panel. All charging is spot on (13.7 on solar 14.2 while driving and drops to around 12.9 at night) so ruled anything to do with battery out. Must just be unlucky, I've put that same detector back in and it seems to be okay! I must say it was very wet that night.