How about using black plastic electrician's tape. You also could use copper wire wrapped around the coat hanger and closest size of shrink tubing,that way there would be no seams from applying tape.
I would think masking off trim and side molding to spray an undercoat and then Allclad would be time consuming.At least with foil you don't have to clean your airbrush.
Bob,
After Googling slot car chassis.It appears,if your car is a 1/32 scale,Strombecker has a mid-motor placement and a 3 screw mounting into the body.Would it be possible to borrow your pic to send it to someone who might have more info?