Update. Cooling the Fridge continued:-
We had some sunny days and some cloudy days, a bit of overnight rain as well. I left the fridge on 5 and it coped well with the heat which was high 20Cs in the van, but a bit less outside with the gentle breeze blowing.
After 4 days the fridge was still going well on level 5 and keeping itself at 3-4C with the wine nicely chilled.
I didn't have a complete understanding of the MPPT reading and texted Roger Donoghue the figures as the picture of the battery showed it as nearly discharged. He explained that if the battery was at, say, 13.8v, nice and full, and being charged, switching the fridge on would drag it down to 12.x volts, and the charger would see this as quite low as it can only gauge capacity by looking at the battery voltage. Switching on your fridge, even with a full battery, will immediately drag the voltage down to 12.2 ish volts. The battery icon isn't a great indicator of charge. It is when you have nothing switched on, and the battery is full, but under load it's not massively helpful.
I had chosen a pitch with a hook up next to it and plugged in on Wednesday morning having arrived on Saturday, it was obviously reading low, as Roger suggested, due to the loading of the fridge. Within 2 hours it was totally full again, so it can't have been down by much in the first place.
I feel much more confident about going without a hook up now if it means that you can camp somewhere nicer, and the fridge will be fine with the solar panel to supply the power.