Trident Maple overwintering questions

[karen82]

I just purchased a nice-looking Trident maple pre bonsai. It's being shipped without a pot and with loose soil removed, but not bareroot.
Should I pot it when I get it, or just wrap the rootball in newspaper and wait til spring? I have an unheated garage to keep it in for now.

Also... I'm moving next spring so I can't plant it in the ground yet. The new house is also in the colder part of zone 5.. borderline for a Trident.
I'm not sure how I will winter it in the new place (it doesn't have a suitable garage); I plan to build a minimally heated greenhouse, though. Would a Trident overwinter better in a 40-50 degree greenhouse, or out in a cold zone 5 winter with the pot sunk in the ground and well mulched?

 

[miker]

If you could keep the greenhouse between 32F-45F (or even 25F-45F, that should be perfect).

 

[karen82]

Thanks. The greenhouse will probably be unheated, but attached to a heated garage, so I'm not sure yet what temperatures it will experience. I will need to keep it slightly above freezing for some of the other plants though. The 40 to 50 was more of a guess, I'm not sure how much it will tend to warm up during the day with the sun shining in.