We'll be using an uxcell 7x4x2" plastic enclosure to mount the entire circuit. 

Start with cutting two large holes for mounting the peristaltic pumps at the bottom panel. I uses a Dremel tool for this work. You can also use large drill bits and a file to smooth things out.

Drill a hole on the side panel for the barrel jack connector that will be used to plug in the power adapter.

Next, place the circuit components (LM2596 board, perma proto hat etc) and mark the holes required to placing nylon standoffs. Drill the holes and screw in the standoffs.

Once the standoffs are affixed, mount the LM2596 module and the Raspberry Pi Zero

Next, attach the Perma Proto HAT on top of the Pi Zero. Notice I am using a large Pi Hat with the Pi Zero, since it gives more space to work with and it works just fine. Affix the barrel jack connector as well.

Once all the electronic components are mounted, attach the peristaltic pumps last, and connect all the wires. Notice we are using the Perma Proto HAT to create a small 12V rail (on the right side) from which the LM2596 and the L293D (Vmotor) draw their power.

That's it, once all the components are wired, attach the clear case top and our dosing controller is ready for some testing and calibration