A couple years ago I build a 10" sub in a sealed box for my truck, and recently broke all the mounts off of the store-bought terminal cup I had used. This definitely hampered sound quality, so I designed this replacement terminal cup to have a beefier frame and mounting flange.
Specs on this terminal cup are:
Max width of flange: 89mm
Max height of flange: 69mm
Max width of cup: 64mm
Max height of cup: 44mm
Cup floor thickness: 5mm
Flange thickness: 4mm
Wall thickness: 5mm
Cup depth: 10mm
Overall thickness: 14mm
This was designed to fit in the same 65mm x 45mm cutout that the original terminal cup fit.
I have been running this cup fairly hard for more than a month now during the heat of summer and can honestly say I see and hear no degradation or breakage in this cup. I printed this version in PLA with 50% infill and it's doing just fine so far (we went through a string of 90°+ F/32°+ C days and it's holding up great).
I included two divots on the cup face to help in locating where to drill, but I did not design any through-holes because it is up to you as to what kind and size of terminal you wish to use (nuts & bolts, binding posts, straight pass-through, etc).
Supports from the bed surface will be necessary for the mounting flange. I printed this with the flange pointed up, but I suppose you could also print it with the flange downward, or maybe even standing up on its side.