a vented cap lets air IN (as gas gets used up), not out...I have had a rubber line from pump to carb (with a metal filter inline) ever since I bought it 10 yrs ago...driven almost 30,000 miles , no problem....
but IF I park my car with FULL tank in a hot garage 95F plus , I get a problem , blew the gas tank sending unit gasket once...I just dont fill before parking now...but a small drilled hole in the gas cap might would prevent that...I most often get a "woosh" when opening the gas cap...