Push caulking deeply into the cracks between the cabinets using paint stir sticks.
Drill holes through the sides of all the cabinets, about 3 inches from the front of the cabinet and spaced every 12 inches. Use a drill bit that is slightly smaller in diameter than the bolts that will be used to connect the frames.
Pass a short bolt through each hole in the cabinets, placing a washer on either side of the frame. Put a wingnut on the other side of the bolt and tighten it completely to fasten the frames together. Begin the tightening process at the center of the cabinet frames and work outward from that point to tighten all the cabinet frames inward to the center of the cabinets.