We purchased the Temp Stick for this exact application. Even plugged in at a campground with the AC on and thermostat set we'd get nervous about a system failure while we're away in high Midwestern heat (100+) with 180 lbs of black lab mix in the rig (100lb great Pyrenees/lab and 80lb golden/lab) . So far this has been a great solution for us. We have a wireless router in the rig that we run everything off of and connect it to either campground wifi, mobile hotspot, or phone hotspot for internet service. We can check it at any time and you can set email and txt alerts based on any temperature thresholds you like... very customizable. I would recommend this solution even if it is a little pricey.
A plus note, it uses very little data because it only "wakes up" from a wifi perspective when it's either out of tolerance or every X minutes you supply... just make sure you place it at "dog height" as opposed to near the ceiling or in the path of sunlight or you'll get false warnings (and minor heart attacks)
