How about wireless sensors with solar power?
This module from Seeed works well. I use it myself to record analog sensor data with a G120 based Cobra 2 board. I have some more in development for a commercial project now that I know it works.
You can use the IO ports to switch remotely too. No processor needed unless you want remote calculation of some sort but the G120 receiving side can do all that.
You can add the battery and solar panel to suit.
This can talk to the G120 if you get the XBee carrier board (Assuming you are using the G120HDR or you can add it to your custom board if that’s the route you are taking)
Wired would of course work and be a little cheaper but you then have the hassle of running the cable and getting power to it. You can then use either CAN bus or RS485 etc. This assumes you will have a processor at either end of course.