In our crawl space, the ground is mostly sand and a lot of the insulation from the "ceiling" is hanging. We would like it to be a cleaner area. We plan to put plywood down to create a floor, but are unsure of how to fix the insulation to stay up, without causing a moisture problem. Any advice?
You can tack the insulation back up, using a staple gun. Smooth the ground surface level, then install a vapor barrier of 4 to 6 mil plastic sheeting. Instead of plywood, consider pressure treated 2 x's, especially if the crawl is damp. They will resist bugs, moisture, etc, and in my opinion would outlast plywood.