My Spider had one, but the captive nuts for the bolts at the rear just rotated in the chassis and so the bolts could not be tightened up, so the back end sagged and scraped on the ground. Undertray is currently in the garage whilst I figure out how to replace the captive nuts. I think the reason there are so many GTVs/Spiders without undertrays is because of the difficulty in getting them off to do an oil change when the rear bolts won't come out because the captive nuts just rotate in the chassis. The mechanics have to cut the undertray to get it off, the bolts are recessed into the tray and if you try to drill them out, the nuts and bolts just spin.
If anyone wants to use mine as a pattern to fabricate a new one, get in touch.