The PYCOM case is a nice one for this project. It's a convienent size which turns out to be just big enough to hold everything. It also has some easy to remove (carefully with an craft knife) cutouts for connectors. But those cutouts aren't always what's needed. Fortunately, the plastic the case is made from is very easy to drill and cut to make custom holes and cutouts.
Start by trimming out some of the molded-in mounting points and wings to make room for our components. The photo shows a case as it comes on the right, and trimmed on the left. The parts that were trimmed out are marked with red. These are easy to remove using diagonal cutters.
Below, you can see that all the cut outs have been removed on one side of the case. From left to right, these are use for the GPS antenna connector, the power barrel jack, and an opening for the BME280.
On the opposite side of the case, we need to cut some custom openings for the air quality sensor. Note the large round opening as well as the smaller rectangular opening. These correspond to the air intake and exhaust of the sensor.
First add the power and antenna connectors. Start by soldering a short length of wire to the power and ground connections of the barrel connector. Slip the wires through the appropriate hole in the case, slide the nut over the wires and secure the connector in place. The antenna connector goes through the smaller round hole with a washer (included with the connector) on the inside and outside of the case, and add the nut. You can use one pair of pliers to hold the connector on the inside and another to tighten the nut on the outside. Just make it snug, be careful not to overtighten it.
Short lengths of ribbon cable are connected to the BME280, AirLift, and air sensor breakouts. Solder wires directly into the header strip holes of the breakouts: no headers required. You will have to carefully desolder and remove the header strip on the air sensor breakout.
You'll need 8 wires for the AirLift and 4 wires for the other two. The AirLift needs wires for: VIN, GND, SCK, MISO, MOSI, CS, BUSY, and RST. The BME280 needs wires for VIN, GND, SCK, and SDI (SDI serves as SDA when using I2C which we will be doing). Finally, the air sensor breakout needs VCC, GND, RXD, and TXD connected.
Now, wire the breakouts directly to the pins under the feather board. You can use the strip of GND connections along the prototyping section of the feather for the breakouts' ground connections. One trick you can do is carefully cut the trace to the 3v strip on the other side of the prototype area and connect it to the USB pin of the feather with a bit of wire, taking care not to short against any other pins. Then you can connect the Vcc and Vin connections of the breakouts to that. Here you can see the breakouts connected to the feather.
The next step is to connect the wires from the power jack to the Feather. And the final step is to connect the GPS antenna and pack everything in.
When everything is happily working, you can use a bit of hot glue to hold the BME280 board, the air sensor breakout, and the air sensor in place inside the box. Ensure the air sensor is positioned over the hole you made for it.