I'm replacing speakers on a fender bassman cab (2x15), and I was noticing it had 4 holes drilled into the bottom of the cab (I assume these were for the original casters). Anyway, the casters were replaced and relocated on the bottom, and I was wondering if these holes should be plugged, or left for porting. It seems that these are the only entrance for air movement in the whole cabinet, and I know that these are listed as sealed cabs. Does anyone have a bassman 2x15 cab that also have these "ports". Or, should I just plug 'em? Thanks!