I have deleted a post by Prof JohnL and the reasons are that the OP asked for tips on how to try and keep a van cooler in storage.
The response was nowhere near the question for the following points:
1. Why was the subject of Insurance even mentioned?
2. Why was the use of aircon used, no storage site has electricity available for use like a site does.
3. Why was the subject of "fit for purpose" raised, it has nothing to do with tips to keep a van cool.
4. Why the reference to "only get the van out at night"
5. Why the question about "wondering why the OP was concerned about heating the van ?
Despite a long reply not a single tip , apart from opening the door and windows to allow the van to ventilate was forthcoming.