Thank you all for the input. I purchased the 6x6's a few months ago and some of them have twisted.
I won't be covering these posts with plastic. The home is exposed on a hill with no shade and the plastic, particularly the railings, did not last long. 5-8 years before failing. Of course, I don't know how long wood will last, hopefully a long time with good paint as the place is for sale. I priced steel for this job and it was over budget.
I picked up strongtie connectors and wedge anchors today and will get after it tomorrow.