I think the key is that the temperature inside the garage (in particular the metal things) doesn't drop less than the outside morning temperature (or the temperature raises in line with outside). In the warmer months this isn't an issue as the building retains enough temperature through the night, it's just this time if year really. I think in winter the outside temperature stays lower outside in the main so less of an issue.
The freezer is a new addition this year, but if anything it will making the air condense on itself as it's sides are cold. I expect it to rust quite quickly, but it was cheap.
An east facing window would help for when the sun is out but that's not really feasible.
And yes, it's detached. If it was attached I'd simply run the central heating through the wall and stick a radiator in it.