The container reduces the hardiness on the roots by a zone or two, but your roots should be native persimmon so I think you will be OK there. For the above-soil part, I currently do nothing to protect my persimmons and they have been doing OK. One thing some people do is paint or spray with wilt-pruf or other anti-dessicant. This stuff is a pine tar substance which helps keep things from drying out in the cold winter winds. I did it for a couple years on my younger trees but it was not clear if it was helping much.

Scott