Update: while foam is fantastic, cheap parts not so much. The relais board crapped its pants yesterday. As far as I know everything was hooked up right. Center negative, no 12v back to the Arduino and really basic stuff. But a couple of couplers stopped working and now even some of the coils are fused? I need to rethink this 12v 5/volt situation.

I got my 12v 8 channel relay in the mail today, so it had to make the foam case for it. While I was at it, I added a barrel plug for the coil power. Foam really is nice to work with. Cheap, easy to shape and glue, soft, light and very forgivable.

This is what I came up with :

Because the relay switches are relatively heavy, I added a top bar. I do not think it is needed as the whole PCB slides into its foam casing. Here you can also see the barrel plug directly soldered to the external power and ground pins with copious amounts of solder.

I remember this trick from an earlier project involving a powered relay board. The centre positive and sleeve fit almost perfectly against the pins. This works for just about every relay board with external power because this layout of +12v - VCC - GND is the most common in my experience.

Here is how it fits together, just like the Arduino UNO test case :

It all fits snugly and nicely. I left the option open to add a piece of foam near the input pins in case I need some relieve for the ribbon cable. And with Velcro underneath I can place it anywhere within the console without worrying it will get loose.