get 4 cheap furniture dollies(I found the cheapest ones at Lowes not Harbour freight), reinforce them w/ 3/4''plywood over the tops, add 4 levels of 4x4 stacked like Lincoln Logs and set the tub on them. The furniture dollies can be bought cheaper than you can find comparable casters and they turn 360 degrees which makes it easier to move it around in the garage.
If you have access to heavy pipe, you can also fab up a rotisserie that allows you to rotate your tub like a chicken to give you easy access to the bottom and hard to spray areas on the top. I have mine up on the rotisserie right now and will be posting pix w/ measurements, etc when I'm all done.
If you have the ability, the rotisserie is the only way to go. It took me a whole weekend to make, but has already saved me 3 weekends of work.
