I have a persistent rust problem on the lower edges of rear fenders where the wheel well liner blocks access to the back side. The lower edge seam wasn't watertight and rust has perforated the outer and wheel well liner sheet metal below the factory sealer bead, which was applied from inside after spot-welding and didn't reach down to the joint. I dug out most of it so I could MIG weld patches without igniting it.
Several local paint suppliers have suggested 3M 08852 Cavity Wax Plus to coat the inside of my larger welded and smaller resin patches to prevent or slow the so far yearly rust lines along their edges. LPS-3 wasn't up to the task, or I didn't coat the out-of-sight area well enough with it. The Cavity Wax comes with long applicator tubes.
I'd like advice on if it really works, and how difficult it is to remove if for some reason it doesn't and I need to weld in a larger patch.
The clerk told me it's better than rubberized undercoating in the wheel well. The suggested alternative there is spray can truck bedliner, assuming it can be removed if necessary. tia
-jsw