This is a quick model I made to hold 4 120mm fans quickly to use them like a small box fan. I used zip ties to attach all the fans and one of those generic 5.5 X 2.1mm DC screw terminals. There is a hole on one side to push the plug terminal into, and it also should keep the terminal from falling into the fan box. (It kind of locks into place when pushed into position)

I use a adjustable voltage power supply to control the fan speed and it works pretty well.

Still needs some work but it is functioning so I will probably leave it as is. If I were to update it I would probably add fan grills and some way to seal off the other side, but for my purposes I just wanted a quick and easy solution.