Agree, put your fridge on a day or two before you set off, pre chill everything at home first before loading your fridge up, run it on 12V while driving and switch over to gas or 240 upon arrival and you'll be fine.
Agree with
@jdove as well reload drinks etc. at night ready for the next day, if you pull up to go shopping switch over to gas while your away and back to 12V before setting off.
We had no problems last year up north in high 30's temps, beers icy cold after driving all day and ice cream was always frozen for the kids.
Dave