The WisBlock Unify Outdoor Enclosure can come with pre-mounted M8 5-Pin and RP-SMA antenna IP-Rated connectors. You may not want to employ these connectors.
You will likely want to use an external antenna, and route an antenna cable to inside the WisBlock Unify Outdoor Enclosure. However, instead of using a connector on the box, you should consider using feed-through cable gland instead. Connectors are notoriously unreliable and lossy, so minimizing the number of connectors is helpful.
You should not need to have a USB connection available for firmware upgrades if you configure your node as a ‘client’, since the nRF52 on the RAK4631 can be programmed (and configured) in this case over-the-air (OTA). However, I note that the iPhone DFU app failed for me until I changed the packet count from the default value of ‘23’ to ‘8’, and disabled display timeout on my iPhone. You really need to make sure OTA programming works before you seal the box. The bad news is that if an upload fails, the RAK4631 is bricked until you reload the firmware via USB. You may want to have a USB connection available as a result.
Another reason why you might want a USB cable is if you want to configure your Meshtastic node as a ‘router’. You will then need USB to access the node. If you route the USB cable into the box using a cable gland, it would be good to have a USB-C data cable that has UV-resistant insulation. A metal-braided cable would be particularly well-suited here. For example: Amazon.com: METZONIC USB C Cable 6.6ft, Type C to Type C Metal Braided Charging Cable PD 65W Fast Charge Data Sync Transfer Cord : Electronics
An M10 cable gland works for both cables. For the USB connector, the opening is too narrow, but with a Dremel, you can split the hard plastic part of the cable gland to admit the USB-C cable. For the antenna coax (to the IPEX connector), the opening is a bit too wide, so you might need to add a grommet.
Alternatively, you can use a ‘split cable gland’. You likely could route both the antenna coax and the USB cable through the same split cable gland. I could not find a good off-the-shelf such product.
Be sure not to power up the RAK4631 initially without the antenna connected. Once it is powered up, you can disable the transmitter in the app settings, and then disconnect the antenna, if needed. Don’t re-enable the transmiter until you have the antenna finally connected.