I just finished building my first UDS and I was debating on if I should put casters on the bottom or not. I like to be able to push it around on the cement but when I haul it in my truck or if I have to haul it out in the yard with lots of snow I didn't really want casters on there to clog all up or roll around in the back of my truck when driving. Well I think I found the best of both worlds since I don't have welding equipment to make a removable bracket with casters. I bought three of these caster dolly's and the UDS will sit right on the top of the dolly and also fit right into the grove it has in the middle and it can't fall off. And when I want to remove the casters all I need to do is lift the barrel up and I am set. I found these at my local Mac's hardware store for $5 each. Just wanted to pass it along incase anyone else was looking for something like this. I will be posting pics of my UDS once I get it home from work.
http://www.mcmelectronics.com/product/22-9124
http://www.mcmelectronics.com/product/22-9124