How much loam and how much gravel for a parking area that also can grow grass?

I’m in Vermont. Very wet. In the woods. Want to create parking area next to my cabin that will be able to grow grass or weeds — not a fine lawn, but don’t want bare dirt. Contractor has available “Shur-pak” which is a crushed stone with stone dust that packs into a hard surface if not mixed with anything. Natural gravel is not available. I am thinking a mix of the existing top soild (scraped off and mixed into the materials he brings to the site), sand and Shur-Pak should work. But what ratio among these 3 materials to create a surface that will support vehicles and grow vegetation?