I have similar circumstance with storage, over the years i have had some damage to young plants as i only throw besheet over them, now that they are mature they do fine without protection in attached unheated garage .
Last winter was the brutal cold one the coldest they have seen since i have had them and they were fine.
If i had small plants such as yours i would try to put them up high and at back of garage away from overhead door with a cardboard sleeve around them for some protection.