Yes, the KBS Strip should have no problem removing the coating from the underbody of your frame. The key with KBS Strip is the be patient and make sure the surface and the KBS Strip are as warm as possible up to 80F.
Can KBS Strip be used on bumper covers without it harming the plastic?
Because of the aggressive nature of KBS Strip, we do not recommend getting KBS Strip on plastic because the KBS Strip could damage the plastic.
If you are desperate, you can always use KBS Strip on plastic, but be incredibly careful and minimize the amount of time the KBS Strip is on the surface. Multiple treatments of KBS Strip with less time per treatment is the way to go.