How do I create a composite surface that represents the LOWEST of a collection of stacked surfaces? (V8i SS3)

Hi All,

I need to create a composite surface that represents the LOWEST of a bunch of surfaces which are stacked on top of each other at different elevations. Kind of like a 3D boolean addition but I only want single surface representing the lowest plane, or an upside down drape mesh. When it's generated properly looking at it from above it should appear as a concave hull. A bit hard to explain but if I were writing an algorithm to do it, this is what it would look like..

Declare a bounding area "area1"

For each "x","y" point within area1

for each surface stacked at this point

if "z" is LOWEST 

set area1 (x,y,z)

endif

endfor

endfor

Can anyone point me in the right direction on how to achieve this?