I have a Goldstream and always run the fridge 2 days on mains before heading off.
I wind the camper up about 15 cm but this is mainly to allow access to the fridge to allow easier loading.
I can't recall,but does your Jayco have a vent in the benchtop? This could be obstructed by the canvas in the wound down position?
It is definitely a good idea to have your fridge cooled down before running on 12 volts.
Grant