The air dam is made of sheet aluminium. Thin sheet can't remember exactly.
I then took the bumper off and placed it on the splitter. Marked out where it needed to go and then went about shaping the sheet
To get it curved I bend the sheet over so its now 90degrees along the whole length and then cut triangles all the way down the bottom half, this allows you to bend the sheet to the perfect shape. I then riveted the airdam to the wood. It's not attached to the bumper just fits real snug.
I don't have to remove the lip but I do remove the whole bumper to get the splitter fitted. I will be making the airdam alittle shorter before I fit it again as it makes putting the bumper on abit difficult.