Sloppy body seam = future rust issues?

[BreatheEasier]

I found this interesting tidbit in the area of the body under the sides of the rear hatch, both sides, where the rear quarter panels overlap and are spot-welded to the body. I can fit more than my fingernail under this area. It should have been seam-sealed, and it seems to be at the bottom and top edges, but that's it. There is no doubt that moisture will get in here and cause issues later. It won't be fun, but the best way to address is to fill with automotive paintable seam sealer, and body color match once filled. What a PITA.