Should I use foam spray insulation in my crawl space?
There are some very good spray foams on the market. Most are a two part system and a starter kit runs around $800.00. This would include the hoses, tanks and spray wands and enough material to do several hundred square feet, depending on thickness.  There are foams that are completely water and moisture resistant as well as mold and vermin proof. I sub out most of that type of work, so I don't have the brand names on the tip of my tongue, but you should be able to  investigate various types of foam and equipment appropriate for your application at your local specialty distributor of insulation products.