weatherproof rj11 joiner?

No at all but instead Scotchlok’s to extend the orginal cables. Been in use and out without additional coating in finnish weatherconditions for 8 years now with success for both my UV and solar-sensors.

http://solutions.3m.com/wps/portal/3M/en_US/EMDCI/Home/Products/ProductCatalog/~/3M-Scotchlok-IDC-Butt-Connector-UY?N=5430432+3294067407&rt=rud