You might take a close look at a larger, flat surface to see if
the powder coat quality is right for your taste. Normally, powder
coating cures to something that resembles orange peel. Although
minor, it may not be what you want on your frame. The motorcycle
frame is small, round tubing so it doesnt show the surface
irregularities quite as much.

I have seen fenders and hoods that were powder coated and
then color sanded and buffed. This really looked nice.

The putty that you are referring to is a conductive filler that the powder
coat guys use to fill weld pinholes, etc. You might talk to the
supplier regarding the longevity of the filler in a mildly flexing application
such as a frame....it will probably work since bondo is commonly
used on a wet painted frame for the same purpose.

mike in tucson