The garage would be way to cold where I am, even insulated in coolers. When it is minus 20 here , I doubt if my garage is more than zero. If they freeze they are goners. Ideal temp for storing is about 40 degrees F.

I place my tubers (bagged in shavings in a box) in my unheated, uninsulated attic. It probably gets into the 50's up there but I've had success for several years. Last year was not one of them though - too mild a winter.

I store mine in ziplock bags of vermiculite (don't close up the bag) in a cardboard box in my garage. My garage doesn't freeze. I have a thermometer in the gargage and I have never seen it go below 38 degrees even when temps outside are around zero. So if you are certain that you don't get freezing temps in the garage, I am sure they should be fine.

I'm trying something a little different this year. I wound up with an extra plastic trash container this year and have layered my tubers in peat moss. The lid can lock on but I've left it loose to allow some air circulation. I'll store in the garage, which should be ok here in NC. If this isn't a good idea and anyone knows better, let me know. I'll let you know if this worked in the spring.

I am storing dahlias for the first time this year and have them in some very coarse moist sand in a card board box in my un heated attached garage. i do have space heater out there for when the temps really drop. So far though its been VERY mild. the dahlias seem to be nice and dormant still. i allow my sand to dry out considerably before i douse again with water. do you think it ought to lift the tubers and check to see that they are still plump? and, just to see if i could, i also am storing some ornamental sweet potato tubers in the same mix. any thoughts on this? anyone tried it with success?
in other news though, i also decided to store some pineapple sage at the same time in a pot and it it is thinking it's spring already shooting out new growth and all :/ i'm not really sure what to do to make it last until about may when it will be safe to move outside. it seems SO far away right now. any help with that dilemma would be wonderful. btw i know this isn't the exact place to ask this question, but i wouldn't know where else to ask and a web search proved fruitless. thank you!!

Pineapple sage is as tough as old boots where I live and will cope with living indoors for a while. Sweet potato should overwinter in sand. It will even overwinter uncovered and dry, in fact, if the tubers are of reasonable size, in the humid climate I live in. I wonder about misting rather than dousing your sand - going for moist rather than wet.

The moist coarse sand method sounds rather doubtful to me especially in a cardboard box. You are in a low humidity area and cardboard box will wick the moisture from sand very quickly. If you place the entire box into a plastic bag and seal it, the moisture will be preserved and you would have better chance. Dahlia tubers really dry out in low humidity areas during the winter unless they are sealed in plastic. The idea in high humidity or low humidity climates is to let the tubers dry for a day or two to the point where they are still firm and when you place them into plastic bags with bit of vermiculite or even some potting soil, that they will stay plump. Too wet and they rot; too dry and they die. Store at the just right stage in plastic and they will do just fine.