Ruggedizing adds weight, there's no way around that.

If I figure that it will take two sheets of 16"x11"x1/8" Stainless (rough estimate, of course, as there is a hole for the screen, and the edges that will connect the two sides) the steel will weigh 5.8 lbs.  Now, figuring a 6.8 lbs Macbook - 2 lbs for the case, we are now at 10.2 lbs.  Figuring about 2-3 lbs for internal mods and the hardened glass, we are roughly the weight of two Macbooks, which I think is acceptable.

In my research, I've also just realized that carbon fiber may be a good material to use.  I will be talking to some CF manufacturers to determine if I can get steel like strength out of it at a thickness that would be usable in the computer.  If so, I may look into it further.