Make sure that slab is DEEP, I would suggest at least 12" to preclude any weird finishes on alloys when machining.
Yeah, you want rigidity, and a monolithic slab is one way to get there. Get with your concrete cupplier to talk about cheaper ways -- they have some pretty high-tech concreted these days. A 6-inch slab cast with fiber across a rebar base (all on top of the appropriate gravel) may be sufficient (depends on a lot of variables, including overall dimensions) and will definitely be cheaper.

Wish I had more machine tools in my stable, but when I do, the slab awaits! <img border="0" title="" alt="[Big Grin]" src="images/icons/grin.gif" />

Randii

Randy Burleson
4x4Wire Managing Editor Emeritus
Mongrel Isuzu Amigo