Does anyone know that giving a datum plane symbol in sheet metal fabrication drawing is mandatory or not ?

I need to give tolerance for the attached parts( Box & Cover ). But i have a doubt that should i give the datum plane ( A,B,C) in the drawing . I need to know how to consider the tolerance value for the mating feature ( clearance fit for both box & cover ) ,either by considering the bending , piercing & punching or Application ( loose fit ).