Thanks K. I was concerned about that as well. However, that's how I got it so I assumed it was factory installed. If it is a problem I'll either buy some locking casters, fab up some screw jacks, or just take off the left side wheels.
That looks great, I am wondering how you will get on with it having two sets of wheels in contact with the ground whilst it is in use, I would be concerned that it would try making off across the garage if not in use but when loading stock.
Let us all know how you find it after giving it a bit of use.