Seems an odd omission for a ruggedised outside modem - the Unifi also seems to not support external antennae.
(I'd also prefer a unifi version just so it fits in the with rest of the networking infra I have in the mökki.)
If you mean the standard routers (like the Rutx50), Teltonika itself sells external enclosures with antennas. https://www.teltonika-networks.com/products/accessories/ante...