I'm sure you guys all had the problem with the bottom level of the rack always being colder than the rest. In my rack I built, the levels are pretty much all even temperature except the bottom. Even the second lowest level isn't colder than the rest above it, just the bottom one. The top level is slightly colder but to no significance.

I would like to correct this, and not waste the level. The rack is closed on two sides left and right, and the front is obviously open to let the tub slide out. The back is also open, and just stoppers to stop the tubs from sliding back too much.

What I did was I closed off the back of the lowest level with some aluminium sheeting. It seemed to help a little bit when I measured it at first but still not enough, but now it's again back to what it was before for some reason.

Anything else I can try other than having a separately wired heating system for just that level?