Nancy, as far as hardiness goes, the clematis should be fine. The large sized trash cans (which I hope have drainage holes--must have since the plants have been doing fine so far) should provide plenty of soil mass for allowing them to make it through the winter alive. During extremely cold winters, you might get dieback on some or all of the top mature vines which might delay their bloom period the following spring but that shouldn't be a problem in your zone.

If you mean by chocolate vine, that you have akebia planted in the same trash cans with the clematis, I would promptly remove the akebia. They can get quite large and their root systems will occupy most of the trash can eventually. Not a good thing for the clematis. If you don't mean akebia, could you give more information on what the chocolate vine is?

The chocolate vine is a Victorian garden plant, has leaves like a Virginia creeper but supposedly flowers with deep maroonish-brown flowers (haven't seen an yet). Yes, did put in drainage holes--wore out a drill bit, actually.
It does grow very vigorously--my mom has some and that's why I wanted it! I'll leave a clematis on one side, an akebia on the other, so each has their own can, then put the others somewhere else....
Thanks!