Pa Farmer - Just something I read somewhere, but I think some folks have used spray on bed liner as an under coating. Probably more expensive than Jon G's brush applied solution, but maybe an alternate option.
Others will chime in to offer more thoughts.
PS - Leaving this thread where it is for now, but it may get moved to the
Paint and Body Shop in the future depending on if this is just going to be used for fenders, cab and other related sheet metal or the whole truck underside.
