I use an Animal Plastics rack that has open sides and back. The back of the tubs get to the correct level of heat, but the cool end drops to the mid to high 70's. I have five air holes in each side as well as the front and back(they are in hatching tubs right now). Would putting a back on my rack help? What can i do to help keep the temps right?

I can cover up some holes on the tubs or put a make shift back or side on the rack itself. What would work?