You probably won't achieve high enough carbonation in a plastic keg as it only holds so much pressure, excess pressure is released via the safety valve at the top or leaks out through the tap washer if theres too much pressure. Best off getting a Cornelius keg which is like a giant bottle or even use 2 - 3 litre PET bottles to save time on bottling. Even in a keg it should taste good, though it won't have the the desired carbonation.