Okay so I'm aware that this is an incredibly common issue, and I'm sorry if this is repetitive, but I do believe I've figured out whats causing it.
While I was cutting out the wheel wells (not fun) i noticed that the outer metal seemed to be fairly intact (strange), which led me to believe that the rusting was occurring from the inside out (dafuq?). Further investigation led me to understand that this was in fact the case, as must of the rubberized coating (rhino-liner, more or less) that protects the outside of the wheel well was in perfect condition. When I removed the rear bumper I was introduced to a vent that uses air flow to pull air out of the trunk for ventilation (aha!). This was my first clue.
When I got under the car, I realized that there is little to no heat shielding above the mufflers, which as you know sit directly below the trunk at a fairly close proximity. Then it hit me.
The mufflers heat the trunk (and its contents) to a point at which any moisture in the trunk is vaporized, and for whatever reason, is not pulled out of the vent (likely due to the aging of the rubber flaps, which then become stiff). Thus, the buildup of moisture has to find somewhere in the trunk to settle, which means the highest, coolest point in the trunk. This would be the tops of the wheel wells, which are the farthest points from the heat source (mufflers). This process, over a long period of time, results in the notorious wheel well rust at the top of the struts.
This is my theory. Give me your thoughts.
T
