Reviving this thread from last year after spending a week in Utah and Colorado camping above 7,000 feet; it was cold. So, I wanted to see just "how cold". I tried to find the Amemo weather station others have used, but it seems to be unavailable. After some searching, I got one of these:
https://www.amazon.com/gp/product/B07L82PF1Z/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
I was particularly attracted by the "Waterproof " remote. Also, ThermoPro is an established company that I have actually heard of and is likely to be around for a while, and they have a range of different products. The unit has a 3-year warranty.
I received the unit and found a couple of difficulties, the most important is the statement at the very beginning of the manual: "Although the remote sensor is designed to be rain-proof, it still must be always put in a dry place avoiding direct rainfall." Also, the remote mounting arrangement is a single key-hole slot making it very hard to mount securely anywhere. Taking a hint from 
TearDragger, I decided to mount it between the water tanks under the back 0f the trailer. To mount it, I 3D printed a little box to hold the sensor; it has two holes corresponding to the temperature and humidity sensors on the unit. I am hoping that the box, and the mounting position will satisfy the "avoiding direct rainfall" requirement.
After checking with Cary about the structure under the aluminum, I mounted the box with four brass screws. The sensor holes are pointing to the side (up in this picture) with only a small gap to the gray water tank so hopefully will be protected from tire spray when driving. There should be enough air circulation to get decent readings.
Here it is with the unit inside and the cover attached.
I mounted the display unit inside with a single screw and a patch of Velcro to keep it from swinging.
The indoor unit is nice, it has a backlight that comes on for a little while when you touch the area below the display. The communications between the remote and the display seems fine, even with the aluminum trailer skin. The display unit takes two AAA batteries; the remote has a rechargeable battery. The reviews I read say the remote batteries last about a year on a charge, so charging at the beginning of the season each year should be good enough; it charges with a standard USB connection, so it can be charged easily; my box can be pretty easily opened with four screws to do the recharge. The display can connect to up to three remotes and will cycle the display between them.