cleaning/sanding undercarriage and bottom of floors and bed for paint

[sircrunch]

What is the best tools to use to clean up under there for paint? I started with a wire wheel, switched to a rol-loc disk, then called "timeout" because it was such a dirty job I'm thinking a good pressure washing would be in order FIRST... I'm finding out there are going to be a lot of places that I can't easily access to brush off or grind/sand.

My truck just has some minor surface rust under there. I just wanna knock that rust off so paint will stick good and last. I figure i'll paint the undercarriage with some rustoleum and a brush. Any suggestions?