Why not use rugged PoE LAN switches? Smaller version has 4 ports (10/100/1000) PoE and some even have 2 SFP ports, all of which working temperature can accomodate the extremes? It cost a bit more than single PoE injector midspan like PowerDsine, but working temperature is pretty flexible.
Some Taiwanese brands (Lantech, Planet, Oring) with 4 ports are still acceptable in terms of price but it's within the rugged ratings. Even KBC networks nowadays are made in Nanjing, China.
I explored these brands in the upper limit only as we have to watch out for the high heat here in the tropics, most of them claiming can work up to 75 degrees Celcius. For the lower limit they claim -40 degree Celcius.