I used a tomato cage but mine had been run over by a tractor so it wasn't exactly round anymore.
But the wire itself is plenty sturdy (and not easy to cut). I just hacked off pieces for a framework -- 2 long ones to run the length of the pad plus a couple inches on each side for legs and a central beam piece to run the width. I laid the bare pad on it, put a scrap of hardware cloth on top of that, and fastened the hardware cloth to the tomato cage wire along the front and back. When I bent it to shape, it seemed too saggy underneath so I added two more wires to the underside going diagonally from front to back. This whole thing was wriggled right back inside the cover the pad came with (I snipped the corners off so the legs could stick out) and stitched it shut.
