Bought 3 of those carts at Northern Tool when they were on sale... I use them at work to roll all of my tools and materials around the job..nice to have everything at arms reach in one place!
They are very sturdy! In fact, I have one out in the garage right now with a Turbo 350 transmission sitting on top and a NP271 transfer case on the bottom tray!
I keep one locked up in the bed of my dually as I'm always moving some kind of equipment or parts, and the cart make things so much easier!!
Currently I only have a interior door blank that I use for building planes/wings,, but Chris's idea of MDF is the way to go. I see a trip to Homies Depot in my future!!