http://forum.ecomodder.com/showthrea...9.html?p=11795
This is my Matrix. I close off all the front openings in the winter, no problems. It turns into a belly breather.
What you see open is with a belly pan back to the rear axles.
I run the air-conditioning from March to November and the temperature gauge doesn't move beyond the normal range.
I would think that with both grills blocked and the bottom open you will not have a problem.