I've never had winter kill off my sage (S. officinalis). Ice, snow, and freezing temperatures - does just fine. Drainage is key to survival. Rosemary, that's another story. I've never had rosemary survive a winter outdoors.

I overwintered an Italian fig (hardy to zone 7) in an unheated sun room/porch for a number of years. Worked well. Probably work for your needs too.

FataMorgana

I have Rosemary in ground, in well drained but wind protected location. I'm in GA, but have to accomodate for colder North winds! The bushes have had snow and ice weighing them down, but survived. Our winters are short spurts of sometimes very cold and sometimes wet weather, but last usually no more than a few days before moderating for another few days. I have brought baby Rosemary plants inside for winter, and they did OK, but did not like the dry air produced by the heating system. Even in winter here, if the plants are in direct sun via glass, they can cook! The Rosemary did survive though. I think both Rosemary and Sage should do OK in a sun room, provided it is protected from winter winds which can be fatal to Rosemary in our area. I found the ones I had indoors needed to be watered regularly with good drainage. Sage goes somewhat dormant in winter but you can cut it back in spring and it grows nicely, for sure in our zone. Looks awful, and sometimes beyond recovery, but comes back nicely. Mint and Oregano will live for us no matter the winter weather. Tarragon is kept in a container on the patio near the patio door to protect from extreme wind/freezing and it has made it through just fine for a couple of winters. I just have to be sure the soil at root level does not reach freezing levels. Tarragon should be OK in your sun room also.