I decided to wrap the 4×4 posts with 1×6s above the deck. It looks cool and makes the posts and railing super rigid. This gives it no room to move in any direction. I notched out for the railing and the horizontal spindles as you can probably see in the pics.
Ran out of Titebond II so I quit for the day. Need to buy some to make some more railings.
-- Derek, Iowa