Perennials for South Facing Window Box in Zone 6B?

I'm really struggling with keeping plants alive in my window boxes!

I live in zone 6B where we get snow in the winter.

Questions:

1. If I plant perennials, will they come back? Or will I have to dig them all out and buy new? (I don't really want the work of having to overwinter and transplant...). I have two 4-foot window boxes and buying new plants every year can get expensive!
2. Are there evergreens that I could plant that would survive year round in window boxes?

Plan:

• I'm thinking of drought resistant plants like salvia, sedum, rosemary, etc.
• I want the lowest maintenance possible.
• I'm also thinking of installing one of those self-watering pipes in the window box. I looked into drip irrigation systems too but I don't like the look of the exposed hose.