Except Toyota has t used fully boxed frames in trucks since 1994... And your last statement makes no sense....
My 05 Sequoia is boxed. And unfortunately, I've had it for exactly 12 years and 1 month, so I'm not eligible for the replacement.
I can't see inside the frame, but there's little more than surface rust on the outside. Kentucky uses salt, but not much of it.
The point of the sentence is that there's a lot of attention paid to the frame because that seems to a common major assembly that failed with these models. If a variety of components were failing, then it wouldn't be so obvious.
I still swear by my Sequoia. 240K miles, 2 timing belts, a fuel pump, and a camshaft sensor. I've got no complaints.