hi there,
on our project we used fresh soil and rolled with a 3.5 tonne bomag road roller when damp. goes down like concrete.
our astro was heavily sanded and the weight help the surface smooth out.
take a look at our track pictures for reference.
don't worry about the overlaps.
good luck....is a back breaking task by hand. best get plenty of man power.
Mark
A.R.C raceway events manager