[crewcabsquared]

I have done several. Clean out all the old caulk, wire brush or grind any rust out in the seams, and apply a rust sealing paint to the seams. Then reapply the seam sealer (3m fast n firm and Crest qwik-seam are both good). I prefer the type that uses a caulk gun for these areas. You can use paint thinner on a small brush to smooth any areas needed (or wax and grease remover). Hope this helps.
Steve