Your right, seam material should not hold water (rust). You can use early Voldswagon Bug fender beading, which is made of plastic material ,and is faily inexpensive. Trim with a razor knife. For body mount pads, find an OLD 600-16 (or so) tire, usually free at junkyards, and cut strips out of the sidewalls, and cut the strips in 2" lengths and it will almost be a perfect match of the original body cushions. My '53 had no pad on the center bolt of the grill, nor the two side bolts to frame (below headlights) but I did put 1/8" pads under them for anti-squick I used old (but new) garden hose washers that were made with laminated rubber similar to tire sidewalls but much thinner. Had them around for 30 years, so not sure you could purchase them now. All you can find is "O" ring types. Good luck--lots of work, but more fun also. Jim