CMC 6.21.5 Any air filter or air filter assembly may be fitted and OE assemblies may be modified. Air boxes and filters must reside inside the engine compartment or in the OEM stock location. Air filter installations intentionally designed to create, or that appear to create a ram air effect are not allowed, even if they were OEM stock.

Nationals or otherwise...I would suggest not putting yourself in the position of having your hard work tossed on a subjective decision. Its just not worth it.