It is also hard to serilize if you get a sick snake in that cag since the roof is the top of the cage and can't be taken off. It is also an easy way to get escapes if it isn't made perfectly since too loose leaves a crack and too tigh often pinches the sides making a twist in the box resulting in a crack big enough for small snakes to squeeze out. If you use heat tape, it can warm some woods enough to let one cage get tight enough so the one above or beloow it to have a crack.
Lidless sliding rack systems are great, but not perfect. I went to sliding rack with a lid to reduce the problems. It is slower, but I find slower a good exchange for safer. If I'm that short on time, I'd just get rid of a coupole of snakes so that I could spend a little more time each of the ones left...lol.
Anyway, I got off topic here. If you want a way to secure the lid on the cage, you can try what I used to do back when I only had 8 snakes in the early 90's. I'd put the lid on the box, turn it upside down, and drilled a small home through the edge of the lip and the top at each corner. I shove a small bolt through the hole (make it a snug fit so that it doesn't fall out), enlarge the hole in the lid so it slid easily over the bolts, and then screw a wingnut down on each bolt to hold the lid securely. I liked it a lot, but it wasn't useful for 400 snakes....lol.
KJ