I did that in the fall to protect the rad / condensor from all of the flying rock salt / slush / sand you name it on the winter roads around here which bombard and embed into the rad fins, never thought about bugs but I suppose thats a good use too. Can't see how window screening restricts much airflow, I guess give it a try like I did behind the existing screening only and watch your temp gauge, I'm sure it will be fine. I simply cut it to fit with a pair of scissors and reached up there from underneath, trimmed here and there, secured it with multiple pieces of landscaping tie wire (stripped off the plastic) and its tight. Has survived the winter quite well. I'll just make new ones prior to next winter.