Cheers guys, although not for the mental image of setting off the alarms.. Yuck
Looks like the Fireangel is winning...
Finding a CO alarm is not such a problem for the caravan, as there is no such thing as safe or bad CO, where as with smoke, there is safe, and dangerous smoke.
We have a CO alarm with an LCD display. We found with the non-display ones we had in the past, in the house, you didn't know what set them off... e.g, the alarm goes of if there has been more than a certain amount of CO for over an hour, or another slightly higher amount for for half an hour, or over a higher level still, for 5 mins. With the display, you can check to see what the reading is, and like Rustic says, then have a look for a source.