Raspberry PI External WiFi Antenna Mod
The Raspberry Pi 3 B+ model has a pad for connecting an external WiFi antenna. You can either solder your coax directly to the pins, or solder a UFL onto the board.
You will need to scrape away some of the PCB to expose the copper for the antenna ground. The strip back your coax and solder to the PI antenna pads.
Now go ahead and mount the RP-SMA plug to your housing and attach an antenna. Make sure that the coax ground and center core are not shorting and are making solid contact. Make sure you are using a 2.4G or 5G antenna.
Finally, you will end up with a timer with a detachable WiFI antenna which should give you a better range. Be careful not to power up the PI without the antenna attached.