Yeah, so how is this even possible?

yes, we also are extremely humid and rainy in summer!
Avoiding water is not possible at all!

 

Wow...that looks like a 1999 Jeep I bought from a guy in NY. I spent about 4 weeks under it with a wire brush, rust neutralizer and an aerosol paint for rust. I wish I remembered what it was called. But I got 80% of it cleaned up. The other 20% was replacing parts.

Edit: Found it - http://www.eastwood.com/eastwood-black-rust-encapsulator-paint-over-rust.html

 

OP- did you go to the beach at all since May?

 

Looks like he did and he lives in Daytona, where they drive on the beach!

 

I suspect it is possible because Toyota chooses the worst framing material available. WTF!

 

No beach driving with it. Like I said, only time I can see it coming in contact with salt water was the 1-2 times I drove through puddles in the boat ramp parking lot. I didn't go real slow through them. Not super deep ones but maybe 6-8 inches. Maybe some splashed up. Mystery to me. I about had a heart attack when I saw the rust though. Just hoping I can get it under control.....

 

Looks like you are not the only person with corrosion problems.

http://nypost.com/2017/08/06/ohio-state-fair-accident-caused-by-excessive-corrosion/