I have some pretty bad roof cancer on my car and i've scraped away all the rust that can be sraped with a hammer and chisel.

For the remaining rust I figured I would apply two coats of Rust Bullit, then bondo the gaps level and then glaze the bondo with a primer sealant. I just don't know which brand to use as the sealant.

If anyone knows or has done this sort of body work any suggestions would really help me.
thanks  

the primer needs to be compatible with the color coats...  

i seem to recall an all metal filled filler to go over rust spots...  but it has been years since i did any body work...

i got spoiled when i worked at a cad restoration shop....  

I would stick with using a regular gray or red epoxy primer. I used a primer sealer for the first time last month. I hate how it sprays and how much sanding it requires to get a smooth thin coat (very thick). This might just be me, but for 25 years I always just used epoxy primer and have always been very satisified.