Check your municiple specs and standards for wiring. Likely a PVC of DB2 comm. duct (whatever one is required locally, and available) should enclose the cable run until entering the unit. Cat5e should suffice, and even if it does fail eventually, you'll be able to repull a new one in that event.
I don't know about all of this, I have used standard solid pvc cat 5e wiring (cat5e riser) on the outside of my house for years and it works just fine. I have snowy winters, rainy springs, summers, and falls.