My rack used to do the same, there is a lot of line loss with cheap wire I re wired all mine with heater cord and that helped some the other thing is if you have a string of flexwatt off a line try running the first to the plug at the bottom and the last at the top the top is always going to be the warmest and bottom the coldest. I actually don't use the top and bottom most drawers. I find the rack to be much more work than the enclosures I have, when I finish some of the reno work I am doing (if I finish it seems like it has been forever now...) I will add some more enclosures and transfer the last 3 snakes to them.