Update 4

Here's a few pics of the 2nd unit's case.

This time, I just cut up the existing base. Much easier that way. My cables were not folding as nicely so I actually cut the hole out a little bigger than this picture shows.

I used a DB25 like TRMPyro sells. This one came from a ODA style Merlock that I converted to a Salzman connector.

Luckily my Crimper I use with the Salzman AMP Circular Plastic connectors works well with the dupont crimp connectors. It's not the exact model designed for the dupont connectors. Unless you have like 3 hands, you need a ratchet style crimper. You can load the crimper with a connector, then add the wire and continue the crimp.

All the cue wires are crimped. The top wires are all grounds.

I've put the crimped connectors into the 7p headers. I tied all the grounds together and put a little heat shrink tubing over them.

Here's the completed case. Notice that the DB25 mounting plate puts the connector a little off center. (Lower in this case.) That's a good thing, as the cables go straight in under the 18M instead of into the side of the 18M.

TRMPyro has the DB25 connectors on his website at http://www.trmpyro.com/firing_panel_components.html

I found that these wires had a little more excess cable to fit together when putting the 18M into the case.

I also found that if you try to use wire larger than 22AWG (like I did for the grounds), they are harder to put into the 7p headers. It's better to use 22AWG for those connectors.

One more random tip, you want to make sure the 18M sits all the way down on the foam. If it sticks up at all, you won't be able to have the key in the 18M with the lid closed.