This would fall under the "any help" catagory, but here it is... I have always thought that it is crucial to have air flow in a crawl space. If you do have vents to the outside, good. If not,you may want to post another message to see if anyone concurs. If the ground is soft dirt, I would put the plasic down first. 6 mil poly is pretty tough, and you won't get nearly as messy with it there. I wouldn't be too concerned, however, about any moisture that the insulation was exposed to until you put the plastic down if you decide to cover the ground last. The insulation breathes, and it will dry out nicely when the project is complete, again provided there is proper air flow.