Portable Fridge/Cooler

We would like to buy a small portable fridge/cooler to keep in the TV when travelling. Probably an AC DC one. I looked at the ones in Canadian Tire, Wal Mart, etc., but, need more info on what works best. We don't want anything too big, just one about the size of the TM fridge, but, portable. One that can keep things frozen and/or cool.
Perhaps some of you have some ideas/experience that you could share.
John
2003 Montana AWD - TV
2004 TM 3023