Storage

[Timelord]

I do not see that you could keep the temperature low enough without some form of refrigeration. The issue would be the general ambient heat over time. If the temp level is pretty constantly high for days at a time, then the general ambient temperature surrounding the box would slowly raise its temperature over time. Insulation would help with shorter temperature fluctuations and a bit at any time, but I do not see it being adequate to do the job over a longer and constantly hotter period. The resultant average temperature would still be too high for foodstuffs etc. You could try some low level of refrigeration if that is your only storage option. There is the electrical method and also there are some physical methods of lowering temperature through liquid evaporation. If you could capture rainwater in tank at the roof level and then use this to evaporate through a porous surface on the storage container, like a porous ceramic, then the heat on the roof would actually help to evaporate and run the cooling process. If the heat is from lower floors within the building, then insulation may perform better but again the above problems will still apply to some degree.
Can you not dig a storage compartment into the floor if nowhere else is available. I know this is not usually practical, but it is effective and if space is limited, then it is one solution. Of course landlords are not fond of this type of home modification. :-) regards, TL