75north

The Dwarf Namwah is a better choice than the Cavendish. I've had multiple D.Cavendish plants lose leaves at 40 degrees, which makes getting a bunch of bananas off of it tough even after it warms back up. Namwahs have shown no damage at all down to 32 degrees in my yard.

Another route you could try is something like a Veinte Cohol. Its cold tolerance is similar to the Cavendish but grows quickly to only 5-6 feet and the fruit fill in in only 40-50 days. If you start in the spring with a 2-3 foot plant you should be able to fruit a VC before it cools down.