they will freeze up the motor with the ones which cool 16 below the outside temp if left on over night i used mine from 8-10pm and then switched off. I had no problems it kept cool over night! The camping gaz was the make.
We have a camping gaz coolbox and we leave it on 24/7 and have done so up to 2 weeks. Occasionally we have had to deal with water collecting in the bottom through condensation and once the vent frooze up but it is pretty good and is beeter than some of the more expensive camping fridges.
we have the blue electrolux with grey lid one. always on, all the time, either gas electric. Although our last trip on electric it stopped woring. could this have been because it was too drafty?. it worked fine when we got back home.