What to use to fill in small holes in metal

Heres my two cents on how to get by on a panel with out doing it the right way.

Sand Blast lightly and carefully until all rust is gone, immediately prep with methyl alcohol or acetone or m.e.k. Immediately shoot bare metal primer according to directions. Allow to dry for a few hours. Then fill with fiberglass reinforced bondo that specifies "apply directly over metal" such as one with lots of zinc. Or skip the bare metal primer process. Thats a way to do it with out replacing the panel and will last 10 years if done carefully, so long as there is not rust coming thru from the back side. .

I strongly recommend sand blast or similar blast rather than wire brush (wheel) as the brush cannot clean the pits and divits in your metal where blasting can reach all pits and divits. Sandblasting can warp a panel so take it super easy on large panel areas

There are some 2 part spray polyester fillers that probably can be put directly over bare metal because they are designed to do so. In that case I would prep very well with blasting and solvent cleaning then fill to hearts content with spray filler. Dry sand rather than wet sand, then use regular 2 part filler primer over that and wetsand...

One problem you may have is the inside or backside of the rocker rusting. The rust may come back out from the inside even if you do an awesome job on the front side. You could cut a hole in the end of the rocker and sand blast down inside the rocker then spray an epoxy primer up in there or rust preventer paint / primer up in the "tube" that makes the rocker. I am pretty sure there are add on hoses that make your paint gun like a telescopic sprayer for getting inside frame rails and rockers.