Is this rust anything to worry about?

yes, it is and it is quite easy to find some around the house, as it is present in many products and foodstuff

Rust killers are concentrated phosphoric acid

 

Just finished the metal prep. Used degreaser, then metal prep (kills rust and etches metal), now onto painting it with POR15. I also bought a small can of gloss rustoleum to paint over the UCAs and some of the rear suspension that gets exposed to UV rays. There's a body lift on the truck (not by preference, i bought it that way) so some light gets under the wheel wells in the morning and evenings. Skid plates are done, and I tested the process on the spare wheel.

 

Update pic