Inside of my front fenders looked a lot like yours. Surface rust, no rust through. I used Fluid Film kit a purchased on Amazon.
Leaves a greasy coating that will last. I applied mine two years ago and it’s still greasy to the touch.
This kit includes a 19” tube with nozzle that helps reach in side the “triangle”.
Fluid Film 11.75 Oz Undercoating Protection Aerosol Spray Can Black 3 Pack, Rust Inhibitor and Prevention, Anti Corrosion Multi Purpose Penetrant and Lubricant, Extension Wand https://a.co/d/9WbnEeh
Leaves a greasy coating that will last. I applied mine two years ago and it’s still greasy to the touch.
This kit includes a 19” tube with nozzle that helps reach in side the “triangle”.
Fluid Film 11.75 Oz Undercoating Protection Aerosol Spray Can Black 3 Pack, Rust Inhibitor and Prevention, Anti Corrosion Multi Purpose Penetrant and Lubricant, Extension Wand https://a.co/d/9WbnEeh