To electrically isolate the part, I would have the piece Line-X'ed
http://www.linex.com/ or use another brand of professionally applied truck bedliner (Rhino-liner?). These coatings are usually a two-part polyurethane and are applied in thicknesses ranging from 1/16" to 1/8". They are TOUGH and once you apply them, they will never come off. Go find a location in your area that applies these coatings, drop by and explain who you are and what you are doing- ask if they can hit it with a coat of product the next time they are spraying it for a customer (makes it convenient for them as they don't have to go through the equipment setup and cleaning for one tiny job. Offer to put their logo on the part or on the robot if they can do it free of charge- I know they always have stickers they put on vehicles they have sprayed.
You may be able to use one of the rattle-can bedliners sold in autoparts stores but they aren't as tough and don't have the same kind of build/thickness that the professionally applied 2-part products do. If you go this route, I would recommend the bedliner sold at Carquest under the name Plastikoat.
http://www.plastikote.com/products/T...ner-Spray.html
I used this product on the interior of my Iltis and have been very impressed with the application.