Rats are smart give them an opportunity and they will take it. As long as they are properly fead and have access to water they won't go to far if they do get out. I have always had success with luring them with food to recatch them.

I have wanted to switch to a rack system but I like the height my plastic bins provide for that exact reason, they can't jump out too easy. I find I am running out of floor room so I might make some shelving unit to vertically house the bins instead of stacking them on top of each other.