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Take your taillights out, and you have access to the area above the wheels to clean. POR 15 is a good product, but it is an "after the fact" product. Meaning that you have to already have rust present. Better bet is to get in there and oil undercoat or spray Fluid Film to prevent the rust from happening in the first place.
So here's the picture of inner wheel well looking up from behind the drivers rear wheel. The black part with the cross pattern on it in the lower part of the picture is the back side of the plastic wheel well liner. Right above that is the inner wheel well support. Where the arrow is you can see it is just spot welded to the rear fender and that is where sand/salt will sit and rot the wheel wells from the inside out. The idea is to get the hose up in there to rinse out that area thoroughly. This is also the area where the foam is placed in the 3rd gens. Looks like they left it out on the 4th gens. Also you can see there isnt much for corrosion protection anywhere in here.

This will work and is a good idea. Much better than hacking and packing it. Just make sure you grind all the rust off before you prime/paint or it will come through again. Good luck!I was just given a 1995 larmie 5.9 L v8 magnum from my grandpa. Its my first car and ive been working on it with my dad, but we have came to the part where the door panels are a little bit rusty. we were just thinking about removing the rust and welding metal to where the rust was and priming and painting it. Good idea or ....?
just an extra FYI.... NEVER use silicone on a painted surface...actually will create rust & corrosion