Boise, ID (zone 5). I'm encapsulating the crawlspace both as radon mitigation and to reduce heat loss (currently no insulation down there).
Under the floor joists are some beams supported by 4x6 posts. Some posts rest on concrete piers, but some rest directly on the footing. I think posts resting on the footing is unusual because web searches don't turn up any other examples of it. One of the posts has some rot at the very bottom; I think that's due to a very local moisture source because there's no rot or moisture problems anywhere else in the crawlspace.

My question is how to seal around these posts. If I run the vapor barrier on the front side, the seal is imperfect on the back side, plus the post will be trapped behind the vapor barrier and unable to dry. But, I don't see a good way to get the vapor barrier under the post, and if I did it would be very difficult to seal where the poly meets the wall behind the post.
How should this be done?