Roadpro have a TRAVEL CROCK POT that plugs into a 12v socket.  This has a 1.5 quart removable stoneware crock, stretch cord and a glass lid.  It sells for under $30.  This is a good option because you probably would have a 12 v socket spare in your truck or RV or  you can plug it into your cigarette lighter/accessory outlet in the car.

There are also crock pots that use gas cylinders.  Coleman Road Trip Propane Slow Cooker has a lot of mixed reviews on the net so the jury is out at the moment on it being a good slow cooker but for heating it would be perfect.  It uses a 1lb disposable propane bottle and has a large 6 quart size crock and what I like about it is that it has a locking lid for when traveling.  The cost is around $78.

If you are out on a sporting event for the day and want to heat your food or keep it hot rather than cook it then the portable crock pot is perfect.  You can use it for hot dogs, dips, chili or any food you have cooked beforehand.

Summary: The advantage as I see it of the Coleman Road Trip Slow Cooker is that it is larger so you can cook for a crowd, when you don't have a 12v outlet, and that you use it also as a regular cooker. I think the Roadpro Travel Crock Pot though would get my vote for overall use for slow cooking results, the price is really good and I think I would prefer to plug it in than use the gas cylinders.

If you have used these crock pots please let me know how you have used them and how well did the food cook.