Quote Originally Posted by Grit monkey View Post
Ok, I've managed to grab a few minutes on sketchup and here is pic of the torsion box.

The method I've used makes for an extremely rigid construction. The top and bottom would be 15mm alu, and the inside of the box would be 10mm alu with the perimeter double skinned to allow plenty for any fastenings.
Click image for larger version.  Name: torsion box open.bmp  Views: 464  Size: 2.93 MB  ID: 10320

Ps, the overall size of the box is 1100mm x 700mm x 130mm
Massive OTT really and you could easily get away with half the amount of material and still be plenty strong enough. Your mate won't thank you either having to Weld that lot. . .Lol

Also You say your short of funds do you know how much Aluminium plate costs.? . . . . Even at mate rates that much plate will cost plenty.!