On Saturday, April 23, 2016 at 3:01:51 PM UTC-7, Fredd Wright wrote:
I have a crawlspace in the basement that has a dirt floor right now. I'd like to lay some sheets of 4x8 plywood (or other material) on it to make a surface suitable for crawling on or putting things on.

For crawling, a few planks of 1/2" plywood (exterior) would be useful.
For storage, consider that you'd like ventilation around the stored
items; I'd try some old pallets, with optional 'wood preservative' painted on
(they won't weather, so stain or real paint are a waste).
I'm lazy, I just strap on some knee pads and a hard hat when it's time to crawl.