on my '51 Chevy, I noticed the lower rear 1/4 peices are in need of replacement, there rusting out from the inside and are paper thin, so I'm going to get replacements for each side, what is the best way to do this, both of the other panals were rivited in place and then I put bondo over top, and block sanded off, should I do the same to this or should I cut out, flange and weld it?