Here is what RCS had to say:
***The RS15 remote sensor is attached to the WDU, of the TZ40, and meant for indoor use only; you’ll need to check with the Z-Wave topology documents [on the Zen-Sys website] to determine if they support the retrieving of OT with the Z-Wave protocol. We, currently, do not make a Z-Wave OT sensor***
Doesn't sound very promising. I think I might investigate getting a weather station. There are no zwave ones, but there are ones that connect to PCs, then also other things are available like windspeed, sunlight, humidity, etc.