Fixing rocker panel rust

[Hood]

My 2012 Fusion has blisters coming up through the paint in the lower rocker under both rear side doors. What is the best bondo/filler or whatever product to use once I clean up the mess? I'm in no hurry because this will be a late spring project.

[jimynick]

Short strand fibreglass filler is waterproof and durable. Grind off the area, tap the rusted portion lightly in (1/4") and fill it trying not to push the filler all inside, multiple coats will be req'd. Try also to cut it before it goes rock hard- and it will, if mixed properly. A Surfoam file and a 40 grit disc on a grinder will be your friend. If you're up to it, it can be final shaped before priming; otherwise top coat it with regular filler to finish. A good putty to fill any pock marks/scratches and you'll be ready for primer. Good luck!