I have brushable seam sealer that I am brushing over all the welds, and using body seam sealer in the areas where there are gaps and where there are factory seams. I'm sure from the factory there was seam sealer schmutz'd in between some of the panels and then spot welded together. But trying to do that here and get good penetration on welds might be an issue. At least that's my take on it... and I'm no expert on the matter.
Gary