With it being winter, and the exhibit in tents outside, how warm is it in the tents? I'm assuming they have some sort of heaters running, but being in the/close to single digit temperatures, I'm sure it doesn't help much.

As long as the line isn't long and they don't make you wait out in the tent you should be fine with a coat. I recommend it being one of the first things you do at the museum so it's not crowded and you don't have to wait in line to get in.

If you have short lines it shouldn't be too bad, make sure you bring a coat, they do have coat check-in inside.

We were there last week & the exhibit was closed due to single digit temperatures

Temps are running about 50 - 60 degrees in the tent. Wear a coat.

It wasnt that bad. But bring a coat of your worried and then use coat check after.

It's not terrible. But there isn't coat check, so I had to wear my winter jacket anyway. Honestly, it's about 25-30 minutes time to get through start to finish.