This is a simple, very useful, solder fume extractor. Just place it upright or on its side near where you are soldering to keeps the fumes out of your face.
Just print, solder the fan leads to the battery case (after feeding them through the hole in the bottom of the extractor) then shove the wires into the cavity at the bottom of the fan holder and press the fan in. No need to glue the fan, it is a press fit.
Then glue the fan holder to the top of the battery case taking care not to get glue on the battery door. I used Goop adhesive, epoxy would also work well.
That's it. Put some batteries in it and enjoy not having solder fumes waft up in your face.
One 60mm x 60mm x 15mm, 5V fan.
One four cell AA battery holder with switch.
Here are four fans at Mouser;
I recommend the slowest, lowest amp draw one for longest battery life and quietest operation. It takes very little airflow to be effective so using a stronger fan is a waste.
You can get a battery holder from Pololu;
Print upright with supports.