Skirting post and pier foundation -- need ground vapor barrier?

[PorkChopsMmm]

We have a post and pier foundation that I am looking to skirt in for winter. We are in zone 5 Michigan. I was planning on using the black ground cloth that blocks vegetation from growing under the house instead of vapor barrier and throwing some pea gravel on top. I thought this would be a better idea that a sheet of plastic because if water somehow gets on the plastic it will have no where to go and become very humid under the house. Our ground is very sandy and is good at draining water.

I would then skirt the structure with hardiboard or some other ground rated cement board and install a few of the temperature operated vents.
Thoughts? Thanks!