Originally Posted by
Sam Murdoch
^ I agree AND double thick the bottom. No sag that way - I'm pretty certain. Adding a center caster or 2 could create issues with balance or moving around if your floor is not flat. If you are using locking casters on the outside corners - the kind that lift up a bit to move - then I might consider simply adding a couple of post feet at the center which would sit on the floor when the casters are down but lift off the floor when the casters are engaged to be wheeled. My 2¢.
Sam