You can bond directly to a panel using a bolt, nut, washer, and terminal combination. If this is for current return purposes a #10-32 can handle 35 AMPs Max, 1/4-28 100A, 5/16-28 200A and 3/8-24 245A. The surface under the contact area must be cleaned to bare metal. The bolt/screw,pressure washer and nut should be Cadmium plated and an anti-corrosion washer of bare 2024 be placed on both sides against the plate to prevent galvanic corrosion. The terminal should be tin plated or nickel plated. The finished build up should be sealed from moisture and the plate finishes restored on exposed areas.