How big does a newly rooted fig tree have to be to be able to survive winter dormancy?  What' s the rule of thumb here?

I have several tiny plants and I was wondering if I should consider growing them inside to prevent them from dying when it gets cold and the bigger trees go dormant.

Pretty cold up there in winter, I do not have anything as cold as you get and I am going to protect all of my cups and 1 gallon plants.  I don't want to gamble on it.

Mine go in the attached unheated garage and I am 70 miles north of you, Don. Most make it through. Sometimes I toss some snow on them.

So keep them above freezing or try to keep them around room temp and keep them growing?

My garage is insulated but unheated? Would that be sufficient as long as it didn't get below 32F?