If I read this right, you are describing a perimeter vent; that is, a very leaky-fitting lid, all around the top perimeter of the box. This is one way to get the passive ventilation I described in my first response. It can work very well. The larger the gap under the lid, the more easily it leaks air, the better it will work. A lid gap of .2" is a BIG vent, if it is the entire lid perimeter of a box this size. So far, so good.
Now, be sure that the bottom venting is just as generous, and distributed similarly. That is, as evenly around the perimeter of the bottom of the box as you possibly can make it, just as with the lid.
You are getting there