Normally if the under tray were integrated with the splitter (one piece) that would be obvious. However, in my application I have a f.g. lip which is separate from my laminate coated under tray. My car is low and sees street use so I need the underside to give a little.
I can assure you that an alumalite copy of my under panel is actually very close in weight to what I’ve constructed. I’m talking much less than 1/2" thick.