I have a large area of my yard that has been used as an RV pad for years. It has been covered in gravel many times and compacted down over time. I would say that the gravel if I were to try to dig it out with a shovel would be several inches in most of the area.

I am not worried about freezing but would like to ask any experts if it would be desirable to pour concreet over this area.

It does have some lower spots and approx a 2" slope. My thought was to form up a 20X30 area and level the forms to a min of 4" at the low side and pour from there.

Would this be a mistake over time or should I level with sand or gravel after formed? Or is it ALWAYS necassary to dig down? Thanks in advance.