Recommendations for Parking Surface for Diesel Pusher

Beware that there is not much that can be stuck more than DP in the mud.
Still remember Prevost rally years ago, where dirt campground had heavy rain at the time and they had to call 6 WD tractor to get those guys out.
Conclusion, don't save on several inches of gravel
Gravel comes in different varieties as well.
Crushed stone can be very unsteady. In our county we do have County Quarry that recycle concrete.
Crushed concrete with mix of dust make very steady base for anything and is cheaper than crushed rock.