Hi Stan - does that part of the operating reefer just trigger a relay, like in the caboose? The TLP222AF SSR is rated for 500mA, so if that part of the circuit draws less than that it should work fine.
The Moteino's I/O pins can source or sink 10 mA at 3.3V (more if you parallel outputs), so you can use them to drive whatever actuator you want, including PWM. I used the SSR because it made the output circuit trivial, but if you wanted more drive (or didn't want to pony up the $1 for an SSR) you could use a transistor or triac instead.
If I was going to develop this project further, I think I'd design a series of little shield PCBs you could stick onto the Moteino for different applications. E.g.
- Powered by DC input or added rectifier/regulator circuit for track-powered.
- Relay, transistor, or triac output.
Being so small (about 1" x 1"), the PCBs would be very cheap.
I'd also design shields for the master node, to read the TMCC commands from a serial line or the Legacy PDI. Installing the master node is probably the biggest hurdle for someone else to replicate the system, because you need something to read the convert the RS232 to TTL.