NHRA general regulations mention "plating" of a chassis, but I am not sure about powder coating.
Quote:
4:11 ROLL CAGE
All cage structures must be designed in an attempt to protect the driver from any angle, 360 degrees. All 4130 chromoly tube welding must be done by approved TIG heliarc process; mild steel tube welding must be approved MIG wire feed or TIG heliarc process. Welding must be free of slag and porosity. Any grinding of welds prohibited. Plating of chassis prohibited for all cars manufactured after Jan. 1, 2003, unless otherwise noted in Class Requirements; painting permitted.
