I use locking lids on the very top of the racks when I run out of room, and keep extras around if I have a new snake come in and needs a QT. As well. I keep around a few extra lids, at least enough for two shelves, as depending on your rack sometimes they can bow and you find you have extra gaps at the top of a tub... if you have a smaller (or very determined snake) it is good to have the option of throwing a lid on to kill the gap (sheets of cut chloroplast work well for this too mind you.

But no, in the racks I do not use them. Having to haul all those tubs out to attend to each snake is too much extra work (spilled water, etc).

Bruce