Here's something we built a few years ago:
http://www.chiefdelphi.com/media/photos/35785
http://www.chiefdelphi.com/media/photos/35786
http://www.chiefdelphi.com/media/photos/35787
On the first picture, you can see a front view. There's a folding door that bolts in to close it up, and it folds back along the right side. The left half has 4 KOP chargers (removed from their cases) and two chargers for our drill batteries. The right has movable shelves. The top is an old butchers block, which isn't going to be breaking.
The second picture shows the left side. We have a built in extension cord, a power strip, and a master on/off switch for the entire cart. There are also 3 fans hooked up with filters installed to ensure the chargers all stay cool.
The third picture is a rear view with the back panel off. The KoP chargers have two circuit boards in them - a small one with the control buttons on it, which is in the front, and a larger one that handles all of the power, which you can see in the back. You can also see how we routed the extension cord into a junction box, and have a second power strip internally for everything that's permanent.
We made two improvements after these pictures were taken - First, we added some relays between the chargers and the battery cables. This ensures that the batteries are completely disconnected from the chargers when power is turned off (the relay opens when it stops receiving 12V on the signal pin), so they don't drain back into the chargers. Second, we permanently bolted a vice to the top corner.
The entire thing is on lockable wheels, and is extremely stable in the pit. It's also built so it can be tipped on its back and slid into the cargo compartment under a normal coach bus.