use either binding posts or some copper bolts. If you want binding posts you can go to partsexpress.com or the bolts at a hardware store. Most people here don't use the cups because it decreases structural integrity and gives a new spot for leaking.
Honestly you might as well just skip the terminals but if you want some sort of terminal may I suggest putting ring terminals on the end of wire sticking out of the box and on the wire from the amp and have them bolt together right outside the box