I just cleaned up my three skid plates last month. The gas tank shield had a hole that was rusted through so I had to patch that up with epoxy and two aluminum plates one on each side of the rust hole. Wire brushed everything. Simple Green to degrease. Rinse and dry. Two coats of POR 15 semi gloss black. Tips: Heat up the bolts before taking them out if they are stuck, otherwise if you break the bolt off in the chassis you may not get skid plate back on. No need to use a phosphate acid to clean the rust. I used it and it stripped the good paint. Be careful not to paint inside the threaded nuts. The POR 15 doesn't keep, so plan to prep and paint any rust spots on your chassis too. Then I applied Fluid Film on everything under the car except brakes and exhaust. I love that stuff.