ohh, that aint that bad, although it still sucks, just use 3 coat of regular primer, thats what I did with my bondo that covered up rust I had.

 

I wasn't careful about the rust when I painted a rusty wheel arch. The rust was back in a month- though bondo and primer.

 

get rid of the rust. if you're bondo-ing it you might as well grind/chip/sandblast the rust completely out.

i like to prime the bare metal, bondo, prim, then paint (with sanding in there too)

bondo soaks up water like you wouldn't believe so make sure to prime and paint it as soon as you can otherwise the rust will show back up.

make sure not to make the bondo too thick, anything more than 1/4" or so is too much.