Building a posh little pergola from 5"x5" bc fir... I would love to stick the posts in a "sonotube" and pour concrete but sure it will last if set directly into concrete (treated with copper naphtalate... Any ideas on longevity? Wrapped in something? What?) I would prefer not to trim out the base as those joints usually open over time, so visible brackets arent an option. Steel plates set into the concrete and up into a kerf in the post, then thru bolted? How tall would these plates need to be? Help me out you salty dogs!