Gravel rv pad?

Our TT sets on a gravel pad which is approximately four inches thick. Over time another layer may be necessary because the stones settle. We use Grade 8 limestone. On one side and the back we have the flat lannon stone and the other side is concrete squares for a walkway. This provides the frame. We've used this arrangement forever for our RV and boat on a trailer previously.
Do NOT use the pretty decorative round gravel as you will never get the rig onto the pad because the pellets just move out of the way and one is always going uphill.