Thank you for your input - meanwhile - My interest is determining what are the limits as far as Moi3d can go to solve the problem, before I venture outside -

There is EvoluteTools D.LOFT http://www.evolute.at/software/software-overview.html

There is Wings 3D https://sourceforge.net/projects/wings/?source=typ_redirect

It would be nice to control the file / polygon count weight / size - some of my files are almost 2 million bytes~

The object is like those inflatable rafts - with a flat bottom - all one piece - top is an open rectangular frame, the hull is closed below.

I'll keep at it and let you know the results.