By coincidence, I was thinking of adding temperature monitoring earlier yesterday.
My reader boxes use a Renogy Wanderer 10A Solar controller to implement a 12Vdc UPS. That and a couple of 15Ah LifePo4 batteries will run an R1000 for about 8 hours.
I have an app to monitor the Wanderers to watch voltage levels on the batteries, and noticed a MODBUS register for temp. Thought it might work as a proxy for the box temperature. It might, but it is skewed high as it is measuring the internal temp close to where the voltage inverters are. So that got me thinking about Impinj, and I had a dim memory of them supporting temperature and had Google Gemini confirm that. Since our concern is less the box temp, but the reader temp, this seems like a good solution.
I have been playing with putting an R1000 out as an early reader 300-500m ahead of the finish line. You can get a pair of TP-Link EAP211 WiFi bridges for about $149Cdn. Good for about 800Mhz up to a km line of sight. Have a simple app that grabs the reads and matches them to the CrossMgr xlsx config file, and displays the group composition of approaching riders with about a 15-30 second warning. Works well, and the finish line officials seem to like it.