As far as I know, skid plates were aftermarket -or at least a factory afterthought, so the hollow tube frame is unsupported where it bolts on. Thus, the tube collapses probably before a reasonable bolt torque is reached. I'd also suspect it would dent in the bottom if the skid plate hit something solid! Adding a small OD pipe inside the frame tube and edge-welding it to the top & bottom of the tube should fix this.
IMHO, a skid plate is worth adding to any Mangusta that's driven on city streets. I have an empty Mangusta diff case in my shop that was the victim of snagging a high-mounted manhole cover in a suburban U.S. street. A 'Goose snagged it at speed and ripped the bottom of the bellhousing and ZF diff-case completely out of the car! LOTS of expensive TIG-welding pieced it together like a metal jigsaw puzzle. The outside looks stock; the inside- wow!