installing screen under Duster's air vent

I just ordered some stainless steel mesh that I intend to install on the underside of the grill that is in front of the windshield. The purpose is to prevent leaves and debris from passing thru the grill and building up in the cavity under the grill. My plan is to temporarily tie the screen to the underside of the grill (I cut access holes in the upper firewall) and support the grill from the underside. I figure I can cut some small foam blocks, wet them with fiberglass resin, place a few to support the top, bottom, left and right ends, and wait for the resin to set. These blocks should be big enough to support and hold the screen in place without blocking the flow of air (too much).

Anyone have a better idea?