Clint, be sure to check that the frame has a good grounding bond cable to the electrical panel. You may have electrolysis causing your problem. One other possibility will be dissimilar metals making contact with each other. I am sure that other members can offer some good suggestions as well.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7