Yeah never mess with terminal cups. They are cheap and will fail. I usually build a box, drill a hole for the wires and use liquid nails to fill the hole. Although on my current box I have the 12 gauge wires coming out the port, even with a 15in sub moving huge amounts of air, the wires don't really move enough to cause audible noise.
Good luck with the work! I will be back up in Michigan visiting family in a few weeks, staying for half of december and a week or so in January. No hope for it being warm then! Nice long drive up there, at least my GTP has a lot to keep me busy!
I will be in the Grand Blanc area, You'll probably see/hear my car around flint when I'm up there, I crank it up quite often, I'm not greedy I let everyone enjoy my music!!!