Well the sides of my rack are closed, it is a melamine rack that is open front and back. Do you mean put black trash bags if the sides are just pillars?
I am also quite confused about temps sometimes. I have thermometer probe placed on the back corner of the tubs. This was put in before I got my temp gun. I find that the temp gun finds a spot in the middle of the hot spot that is let's say, correct at 89 - 90, just that middle spot, if I move the temp gun even an inch it will lower the temp. The rest of the hot spot is like 85 - 86, as shown in the thermometer probe. So what should I go by? That one little spot in the middle?