Can I cover/wrap 6x6 post with plastic to protect them from rain during construction?
If they are treated, they are probably okay. However, I have any easy fix; we had some 6x6 doug fir posts that were going to be out for a while, and we just put some 5 gallon buckets upside down on them. That keeps the end-grain dry - which is where it will absorb the most moisture - without sealing the end totally. Worked great.