Picked up a used "W" brace in good condition and want to coat it with something that will help prevent rust. Tried searching but couldn't find anything... Should i just spray on some rust encapsulation and then hit it with the 3M rubberized undercoating?

attached some images of the brace below

 

Bed liner coating works great because what happens is you end up with a lot of debris sitting on top of and in the cracks of those things. The bed liner is very impact resistant against rocks and crap flying at high speed.

Body undercoating as well but its usually a 2 part epoxy and not as easy to apply as bed liner.

Lastly your u can always hit it with some cold galvanizing spray (aerosol zinc) then flat black primer, definitely the easiest option and it will add an extra 5 years into the life of that item.

 

POR-15 Is pretty solid.