No primer dude,
Your not trying to seal it like in auto body, This is an enamel paint that is not a cured product, ( no hardener or chemical reaction going on) it basically just hardens as the solvents evaporate. Re-introduction of solvents will turn it back to liquid.
Think of it like drywall mud. If you paint over drywall before the mud is completely dry, the paint will form a seal over the water underneath it and a blister will form down the road. Same goes with high temp paints. But much faster due to the temperatures created when cooking amplify the effect probably 500%.
Even if you sandblast the cooker to bare metal, the metal will still absorb moisture before you can get the paint on, and sealing over it will create those same blisters.
Best thing to do, trust me on this, is get it as clean as you can , then apply the high temp paint in light coats , letting it dry very well before each additional coat. A good sunny day under direct sunlight works well.