I drilled 1/2" holes in my hog troughs, flushed them out as best as I could, let them dry for a few weeks, and used Eastwood Internal Frame Coating on them. It has a long, flexible wand with a 360 degree spray pattern, to get top, bottom, and sides. I did this too on the frame at the front spring mount and the rear cross member. Then I plugged the holes with plastic plugs.