We have residential refrigerator too. You do not need to warm up your camper for your refrigerator to cool before you leave. We used an extension cord to power the camper and keep the freezer at proper temp while we loaded everything up for the trip. We left New Hampshire early December our freezer was cold and making ice as we traveled to Florida. No problems, freezer was fine and solar panel kept batteries charged. Of course, we did not boondock... for that, we would need Lithium batteries because the refrigerator uses a lot of power.
If you want to know how long you can power your camper without hookups, get yourself a 'Smart Shunt' (search forum for posts). It will show current usage and how many hours it will take before you reach 50% of your battery storage - on your phone.
2022 Eagle 321RSTS w/Overlander II solar
2021 GMC Denali 2500HD Gas w/Timbrens
PullRite SuperRails & #2700 SuperGlide Hitch