The jointer base is only 17 x 14 so it just barely is sitting on the metal base plates. The rocking is coming from the fact that the base plates are flexing badly, even when the base is not lifted at all.
I may try laminating a couple of layers of 1/2 or 3/4 plywood and screwing that to the frame and see if that helps. I'd sure like to see this thing work as it makes moving the jointer around so much easier, especially since when I finally decided to buy, the price had dropped to $37, so I got a heck of a deal (at least if it ends up working ok).
Fred