Hi:
I put the license plate on my MKII on the mesh and positioned it such that it was on a part of the mesh which was aft of the inner fender-----I figured this was a relatively "dead air" zone, in which there was little or no airflow that would be impacted. Also, this would limit any air pushing the plate outward. No cooling problems or other issues, and I've driven the car about 900 miles in January since doing this. This is in Texas, on both I-10 and around Houston, where a number of days I went on drives were relatively warm (high 70s). I have been really pleasantly surprised by how cool the car runs thus far.
/s/ Chris