Oops! I jumped the gun! I just asked what you would be painting on your other thread!
I would paint the inside fenders first. Anyway that is what I did on my bike..... Since you don't ever see this I used a so-called rust preventing paint, after de-rusting the area....
I did more or less the same under the tank where you never see it.
I just taped off that area, and did not do the best taping off, as no one can see that area, and a bit of over spray does not matter much.....
By doing that I did not have to worry about getting "Bottom Paints" on the Art work after the art work was done.
When it was time to shoot clear, I shot it over all the art work and the bottom paint.
My bike is not HD and so the fenders are chrome, so these were a bit different, but still these were rusting on the bottom side next to the tires, so that was painted, as was the inside oif the head lamp bucket, the arms that hold the head lamp bucket, and any place you don't see normally that is steel and can rust...
My bike is 21 years old, and I don't want to rebuild it again body wise.... Mac