There's a small opening on the front of the plate where it meets the bumper crash bar which allows airflow in as well as the vents in the fender liner.
I've put a few hundred miles on my GX with these plates with no issues. The plates don't completely seal off the area, they are more to protect the washer fluid bottle from large debris, air intake area from large water splashes and of course giving you a place to attach the fender liners if you cut them.
No plans for powder coating right now. I'm a 1 man operation and I with my full time job, adding powder coating to the mix would be difficult. Trying to keep the costs down so folks can modify these if they wish.