Figure the transformer being 7" in diameter. We plan to mount the power supply upright so we will be using a 3U enclosure. That means 5.25" high and 8.625" wide. Two of them will occupy the same rack space as our larger chassis. All of chassis will be 14" deep with the same aluminum X design element.
So... I'd go with 8.5"(W) x 14" (D) x 5.25" (H) per channel as a minimum. Plan on some heatsinking for the UCD700. It may have >90% efficiency but your still talking big power.
Here is the drawing of our large chassis.
