Cut two planks as wide as the dolly your camera will be sitting on.
Drill a pair of holes in both planks, 1 inch in from each 3-inch side, centered across the 3-inch width.
Drill a hole through the center of each end cap.
Secure a pair of end caps to the plank through the holes drilled in the planks, so the caps on each plank point in the same direction.
Cut two pieces of PVC as long as the desired tracking dolly shot.
Secure one end of each pipe into the end caps on one plank, then secure the caps on the remaining plank to the other end of the two pipes.
Lay the track out in the location of the tracking shot.
Place the dolly atop the PVC pipes, with the sets of wheels straddling the two PVC pipes.