I have an 08 sequoia platinum that spent its life rust free in Texas until I moved to Pittsburgh 3 years ago. First winter got rust on frame, rear subframe and control arms similar to what you have. I've just put it on jack stands every spring, hit it with a power washer, then spray with an Eastwood rust neutralizer/top coat combo. I have redone it each year since and seems to be controlling things fine. I have to remind myself it's a daily driver not a show car.

it truly is a beast, the ultimate 4x4 / family hauler / tow rig. 150k miles and nothing but fluids and brakes. ~30k of those miles are pulling a 7-8000lb trailer.

 

I just hit the rear subframe with a wire wheel and brushes. Gonna spray on the degreaser next... then POR15.