So, Foam Mats are easy and inexpensive drawer liners. One day (once I have a more organized workshop) I plan on buying more foam mats and cutting out spaces for specific tools - much like people do with Kaizen Foam. But Foam floor mats are much, much less expensive.
I removed them and then cut a piece of MDF I had to fit the bottom of the cart. Then I screwed the MDF to the cart from the inside. In addition to having a surface that I can easily mount casters to, the MDF adds more rigidity to the thin metal bottom of the cart.
Next I added 4 casters I had that I knew were of good quality. All 4 rotate 360 degrees.
Then I put the drawers back in and moved it around easily. The front 2 casters lock in case I need it to be stationary.
It's a dirty little tool cabinet, but it works great and I love it. So for those of you who do not have the money to buy one of those very expensive tool cabinets from the big box stores, something like this is a great alternative.