This is a fully parametric version of http://www.thingiverse.com/thing:1026128. Its my first stab at openSCAD, its not the most beautiful code, but it works. Its been briefly debugged with some huge values for variables. It is in metric, for now. I would like to have it accept values in fractional inches too.

I made this here: http://www.thingiverse.com/thing:1026128. It works great with 2 perimeters, 30% infill. I use a stronger engineering plastic like Nylon, PET, or ABS.