what are good things to remove rust from inside the frame

[old_1966_GMC]

so what are other good ways to clean and remove some rust inside the frame ive gotten the out side done just need to finish up a few spots by the leaf spring where the wire wheel wont fit, what would be the best methed to be able to clean and remove rust from the inside of this frame im also ganna be spraying it with Rustoleum Rust Reformer and then spray with semi gloss black from vht.

Not looking to use any chemicals neither also i dont have a air compressor but if i did i would not be makein this thread sence i would just media blasted it.