I know the weather conditions here in the UK are not the same as were you are. But I had my models in a storage unit for about 5 years after my separation. And they are now stored in an outside shed. I have not had any problems even with the kits that I have had for years.
The only thing that could be affected is the decals. If you are concerned, you could remove them from the boxes' and store them in a folder which you might be able to leave somewhere else other than the storage unit.
How cold does it get in the winter.
I am a Norfolk man and i glory in being so
On the bench: Airfix 1/72nd Harrier GR.3/Fujimi 1/72nd Ju 87D-3