What about the void below the slab?

Boy, the termites is going to enjoy this. This is the worst thing I can see from a termite control point of view. That complete void below the house will have to be completey foamed with a termiticide when an infestation occurs.

Forget about a pre-treat of the soil, it just doesn't hold up that well with the chemicals available.

How about ground water seepage coming up underneath the slab. Ground water or a spring will find those voids. We have springs out here in the Rockwall area near the lake horribly. You can lift up any object on the ground even in the summer months and find water on the surface of the ground.

Just my thoughts,
rick