your right they are easier. On the rack I built about 3 months ago, I noticed the side loaded 41qt slots I had on the bottom the snake would get there heads between the melamine and the tub. Got lucky and caught one of them just as they were getting their head through. I have since removed the 41 qt tubs on the bottom and replaced them with 28qt..
My tubs go in deep, as I wanted to make sure they couldn't push out. I have about a 3" lip, the tub will not bow out that far. *knocks on wood* never had any issues with escapees.
If nothing ever changed, there would be no butterflies.