If an antenna is expected to be exposed to rain water, then solutions with at least IP65 should be implemented.
Another thing to consider is the storage of the RUT device as it is designed to comply with the IP30 rating, which means that it has no protection against water. Thus it requires additional cable, however, cable itself should not be too long as it introduces additional signal losses, reducing the overall transmitted power.
An antenna, such as the one described in the link, could be suggested. It is a directional antenna with higher gain, better VSWR, it has an IP67 rating, and the router itself can be placed right inside the enclosure. A thing to note is that a additional passive PoE injector is necessary to supply power to the router.