Leave it outside ,but when there will be frost or freeze annonced bring it in till the temperature goes up above freezing.I don't know what else you could do because even my banana is indoor in winter and not dormant.

sam

If it is going to freeze bring it indoors and allow it to go dormant. This way it will save its strength for the spring.
Give it light watering once every two or three weeks and put in the basement. Keep out of sunlight.

It will rest and will do just fine.

The key is to not give it light or sunlight so it can go dormant.

Then in the spring bring it outside a couple hrs at a time gradually until it gets accustomed to the bright sun. If not it could go into shock and stop growing or possibly die back.

Here is a link that might be useful: growing dwarf trees

In zone 8, I would put it in the ground and mulch it heavily. If it was growing in your area I'll assume that its hardy there. Let the cold kill the leaves back and then use them as natural insulation around the trunk (bend them after they freeze back) then wrap frost cloth or a blanket around the trunk if there is going to be a freeze. If the trunk gets hit by a freeze (turns to mush) cut the mushy part off and continue wrapping. Your main goal is to protect the trunk as much as possible, if you don't cut the mushy part of the trunk off it will spread down and rot more of the trunk. I have photos I could email you of mine and what I'm doing with them (I have about 50 in the ground) I am in the same zone as you.