The safest course would be to provide some root protection for them. May not be necessary in most Z6a winters, but no harm in having it. As for where...

Fully dormant plants do not need light, so that condition does not disqualify the crawl space. Watering should also not be necessary. Wrapping each pot with bubble wrap or another type of insulation then placing the pots close together in the barn, then wrapping the whole should be fine, too. Placing a large carton - I've used rigid styrofoam to make a "carton" big enough - over everything to capture some ground heat is frequently recommended but would not be relevant if there is no ground contact between the barn floor and the earth. You also want to be careful of mice and voles. Some years they do not present a problem, but last winter I found voles to be a major headache. Trapping is probably most effective.

Thanks so much for your reply! The floor of the crawl space is dirt, so I was thinking it probably will not freeze too hard under there. I'll see what I can do about wrapping the pots. Critters could be an issue, though, I'll have to keep an eye out for them. Thanks!