I went with your disired thickness but a must is the 6 bag mix.
One think that I did and not regret one bit was to install anchor tie down points.
I used 1" cold rolled bar stock that I heated to bend them like inverted U shape with long horizontal tails. These are about 3 to 4 feet long and I went with addtional rebar weave mat and and additional 2" thickness 3 to 4 feet around each tie down. I used a cast iron water main shut off cap housing so I have a covered flush floor tie down. I have used these for pulling vehicle frames and such.

I also went with water heating coils underneath the washed sand that has been heated by a simple water heater two 5500watt elements. I have used this system for 14 years now in NORTH DAKOTA!