In your climate zone there is no need to bring it indoors over winter or to pot it for a full year at all. A few months to grow to gallon size is fine.

It would be more likely to die in your garage than outside in a pot. They are outdoor plants.

Agree. Winter over clems all the time in 1 gallon pots outdoors and unprotected. NBD

By fall it should be large enough to plant out. If you are planning to plant it in the ground in the long run, due to the decreased heat and water stress on the plant in fall's cooler temperatures, that would be a great time to plant it in its final home.

For my first clematis and learning how to care for it, I had a clematis in a 1-gallon since spring 2013, and I thought it probably would have died over the winter, but it certainly came back, and that is including this harsh winter where so many people had plants that died.

So if I had it to do again, if I did leave it in the container, I would probably mulch the container throughout the growing season and including winter, and also might go to a 2 or 3-gallon in the first season because I didn't know how well a 1-gallon would do, but just know that 1-gallon worked.

When I did transplant it in the spring a few weeks ago, the root ball was not that big and did not fill the 1-gallon, so it probably could have stayed there for another growing season, or perhaps I could have done other things to help it grow better in the 2013 season. It is now about 24-30" tall with 2 primary vertical vines, so I think my lack of knowledge on how to care for it in the first year did not detrimentally hurt it.

Most Clematis are hardy down to zone 5 so there is no need in zone 8 to take special precautions over winter.