I'm impressed, it looks good!
I have a couple of things...
First, cost is reasonable. I know what I can bring one from Europe for, albeit they were downright snitty about it because they made it for European vans, not for the Promaster, with either it's diesel or gas engine, and they made no bones about being insulted that I would "alter as needed" the product to fit or add the required cutouts for the gas engine in ours. After speaking with others in the automotive trade that deal with many European folks, that's an affront to them to "alter" their products, after they spent the time, effort, and pride in what they do to make it. I can appreciate that. BTW, their's was made from 16Ga stamped steel, if memory serves.
Second, the purpose of our skid plate is the "trail roads" that have two tire paths with a high center section that grass and other weeds grow in. So that debris getting in those ventilation holes and up against the exhaust manifold IS to be an issue. Been there, done that, so has everyone else that remembers the first days of catalytic converters with the perforated heat shields, and ranchers trucks catching a hay field on fire. Grass in the shield was the problem.
Finally, an observation we found the hard way. We drove our Promaster down 4 miles of absolutely gooey muddy road last fall, for the first time. At 10mph it was all we could do to keep it on the road. I immediately headed for the car wash returning to town, and spent 4 cycles washing mud from underneath, because washing off WET mud is MUCH easier than dry mud. All of the effort went underneath with me on my hands an knees in the wash bay, and I sprayed up front underneath, too. LITTLE did I know until a week later, when we took the van for an oil change, the mechanic asked me if we had driven the van into a muddy ditch, because the lower of the two radiator fans was blocked from running due to mud tossed by the wheels. I still cannot understand how that happened, geometry-wise, and would not believe it could had I not seen it for myself.
I must then ask myself why Chrysler removed those two plastic sections of "skid" plate from production models and only left the one side piece in place??
SO...think about those things also in your design. while allowing proper ventilation, strength, and any other factors.
To date, we're still driving VERY carefully off paved roads. Keep us posted on your design and progress, and THANKS for posting!