Ok, you need to either hex or put a key way on the wheels. If you go with the keying idea. You will need to add a hub to the wheels and have the hub bored out to the size of the toughbox shaft. Add a keyway to the hub and your done.
Hex would be my preference. Make a hub that has a hex on it. You will need an arbor and broaches. On the toughbox you will need to make a custom shaft aka hex shaft. Since Andy hasn't released the hex bearings yet. You need to either turn down the shaft to a 3/8th's hex or make a 1/2 hex shaft. Get a bigger bearing and buy a hex sleeve for it.
Need more info,
email me.