Crockpots can be sourced inexpensively (~$5) at thrift stores and can use relatively small amounts of power. In addition to the normal use for stews, chilis, roasts, etc, a crock can be used to bake bread, cornbread, pizza, heating water, etc.
Less-expensive crockpots tend to 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.
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 before purpose. For this reason buying a used one at a thrift store may be preferable.
Some general trends:
Note that you can use a high-power crock on the LO or MED setting which will use less power.
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 ower means the crock's wattage is not particularly important.
Crockpots can also be used with 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.