12v crockpots do exist2) but they tend to be rather expensive.
Used home crockpots are available for cheap at thrift stores everywhere, and even new analog ones are inexpensive (see below) As a bonus, analog crockpots can be run on cheap-and-simple MSW inverters; below 100w they can be run on inverters powered by the ciggy port.3)
The power consumption of the crockpot is of great concern, both for adapting recipes and for powering the device for the hours it will be running. Check the wattage information on the bottom of the crock (used) or packaging (new) before purchase.
Some general trends:
Because the crock power and size are related, a crock on HI (or LO) might cook similarly, regardless of size. The larger one would just cook more food if you needed that. Having said that, very small crocks, such as those for nacho cheese dip, may have a single, underpowered4) setting and so may not practical for actual cooking.5)
Also note HI/LOW on different size crocks tends to cook similarly as the wattage is designed by the engineers to match the size. In the examples above HI power is rated ~50w/qt.
Crock-pot / Rival has said in Amazon responses that
All of our current slow cookers do cook at higher temperature settings than our old ones. The Keep Warm setting is approximately 165 to 170 degrees F. Both the Low & High settings cook at 215 degrees F., but they cycle differently. Therefore, the High setting will still cook the food in a shorter period of time than the Low setting will.
In 2015 they were stating 209F, which lines up with the statement above.
Analog crockpots have simple hand dials to control power settings and run nicely on less-expensive MSW inverters.
Digital crockpots have electronic pushbuttons and often displays. These will likely require the more-expensive PSW inverters.
As we've seen above, larger crockpots tend to use more power. But the physical size of the crockpot is an important factor for those living in small spaces.
Even if you have the power to run a big oval 250w crock do you have counter space to run it, or space to store it when not in use? If needed, measure your spaces with a tape measure and bring it with you to the thrift store.
Some crockpots have permanent crock linings that cannot be removed for cleaning. This is less important in a vehicle than it would be in a house with a dishwasher.
If buying used, buy whatever is priced best and otherwise fits your needs. If buying new, the removable type may cost more for no practical benefit.
There are millions of recipes online for crockpot cooking. Use search terms like:
also see the further reading section at the bottom of the page.
People who charge with an isolator will have excess power while driving. For decades RV people have put a crockpot in the kitchen sink and cooked with it while motoring down the road.
Using alternator power means the crock's wattage is not particularly important.
Crockpots are a good fit for solar power. With lithium batteries this cooking can happen at any time. With lead-chemistry batteries cooking needs to be done after the bank is mostly charged and there is excess solar power. This is usually around noon when most crockpot dinner recipes will be started anyhow. It does mean that the crock may be less useful for breakfast and lunch cooking.
On cold days a running crock can be “free heat”. Conversely, on warm, still days you may want to cook outside. Be aware that windy days can wick too much heat off the crock when outside.
Because the contents are often wet and steamy, crockpots are usually fairly easy to clean. You might lightly oil the inside of the crock before cooking something sticky, or line with foil. Parchment paper is a common liner for baking in the crock and can be reused until it tears. Disposable crockpot liners do exist but tend to be expensive.
on cold days you can run your crock a few minutes then proof your yeast-risen doughs in it. Perhaps put it on the dash in the sunlight with the clear light on to keep it warm without overheating.
Some leftovers reheat very well and evenly. They can be dumped into the crock, or placed in a foil packet. You may want to preheat on HI for a while then set it to LO a couple hours before you want to eat.