First step is look at air flow from the lower area to upper, on the working side. Make sure there is no path except thru the fins, or the burner stack. Best if you have a baffle that slopes up from top of the vent opening to the fins, so air will flow up to replace the air that is heated by fins.
Then go to top. You need to install baffle so the heated air from stack or fins can go no place except outside. And should all slope so there is no place for the air to pool. While you are at it, extra insulation between the cold part of fridge and outside wall will help.