I built a DIY front undertray for a Miata I used to own. It incorporated a 1"-1.5" splitter as well, as the nose of the car easily allowed for the addition. I extended it rearward to the cross beam of the engine cradle, as wide as possible from wheel well to wheel well without the tires touching at full lock, and as close to the control arms but with room for them to move without interference. Driving without it and with it demonstrated it had an enormous improvement on front stability at highway speeds. Can't say I noticed an improvement in engine cooling, but one must be cognizant of not making the tray so long that it blocks airflow through the engine bay. A heat extractor hood was eventually added, and the front stability and coolant temps were again significantly improved. So much so that I had to add a rear spoiler to compensate. I used 1/8" black ABS plastic, and it held up quite well, even in parking lot dings. If I had gone more than an inch or two longer on the splitter, I would have added supports, but I think less than 2" of splitter won't require additional supports. I think the V would require 2 pieces; one behind the front air dam and a second piece in front for the splitter. I think if tabs were left on the ABS, they could slide into the existing slots for the air dam, and once secured with fasteners, provide additional front aero. Again, I wouldn't go overboard on the splitter length, or supports would have to be added.
If one built a tray behind the front air dam, either the existing factory tray would have to remain intact, or the DIY tray would have to be secured to the existing panels so that at least the current level of sealing in front of the radiator were maintained. Airflow leakage around the front of the radiator is a significant factor to consider.
One good thing about 1/8" ABS is that a heat gun on a low setting is good enough to mold it to tighter shapes without much effort. Too much heat will bow or melt it, and weaken it.