[Rederrabbit]

After removing the rocker trim to install rock rails I noticed water dripping out of a couple of the holes in the rocker panels which seemed odd as it hadn't rained in a couple of days and the rest of the underbody of the vehicle was dry. Upon further inspection I could see through the holes in the side of the rocker panel that the front and rear were filled with foam and the foam was sopping wet like a sponge. Does anyone know why there would be foam inside? Definitely not a place where you want water to collect and not drain out. I have seen many rusted out rocker panels.

 

[Harbor]

The foam is sound deadener. Dodge Challengers have the same rust issues from the wet foam in the front wheel wells.

 

[Rederrabbit]

Photos inside the rocker panel from an inspection camera. Everything looks well coated but a little rust starting.

 

[WisHawk]

I would suggest getting something like this and spay everything down real well before putting you rock sliders on.
I have used this on all my vehicles and I am very happy with the results. A couple coats on all exposed surfaces. And take the plastic straw and spray up into door panels and rocker areas were ever you can reach. I tend to get a little crazy with it. You may have to re-apply on some of the more exposed surfaces after a winter, but it sticks very well and is not sticky after it drys. Drys to a clear flat finish. They also offer it in black. 2 cans was more than enough for my JKU and I used 1 can on my trailhawk.
My 2 cents.

RP-342 "HEAVY" Military-Grade Rust Preventive Spray

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