I bought a wireless tyre pressure gauge a couple of years ago, which worked perfectly. When we sold the camper we transferred them to a car. They were removed easily by first unscrewing the locking nut then the sender unit. We now have 2 cars with the gauges but the tyre senders have corroded onto the valve in just 6 months. This took a couple of hours to cut off with a hacksaw and consign straight to the bin. The screw-on sender has brass threads as does the "antitheft" locking nut, and I assume the valve is also brass ?? Why has the corrosion taken place so rapidly? And is there a solution to fitting what is otherwise a great bit of kit?
Dissimilar metals will often corrode quickly when threaded together, a smear of copper slip will help.
That white powder looks like aluminium is at work. And you never drove the camper on gritted roads, but you did drive the car. And you damaged the dyed anodizing or brass plating on the nuts by using them before. Solution: pay more for better QC than the bazaars of Shenzen. Or replace the locknuts with a proper brass nut or leave then off and use green loctite (almost impossible to undo .. the blue is totally impossible AFAIR).. as it looks to me like thats the cheaped out aluminium part.