I got some FM frame rails from their deal of the day last week. While I'm under there I want to clean up some surface rust from some scrapes. Should I sand it by hand or wire wheel? I'm a little nervous about possible sparks near fuel filter, etc. I'm going to slap some rust bullet on and re-undercoat it afterwards.

 

Light wire brush by hand, then coat with POR15. Undercoat over that, and you should be good to go.

 

Sparks by the fuel filter, forget about it!! No worries man you wont explode.