It depends so much on the outside temperature, which side of your van is
exposed to the sun, how many times you open it, your question is difficult
to answer. The fridge can only cool to so many degrees below ambient
temperature.

For instance, on my recent trip, during the day while running on propane,
my fridge would be about 7*C in 25*C heat, with exposure on the west side
of the van.  In the morning, the temperature in the fridge would have
dropped to 0*C, as the outside temperature overnight was about 7*C.

FWIW
Keith Adams
calgary.ab.ca
86 Westy and some other random VWs