Given all of the short cuts and crimp connectors and crappy whatnot used in my camper- I have the hardest time believing that someone on the factory line would actually take time to solder something.
X58 (or how many separate pieces of wire they used in my A-Frame). I guarantee that whoever performed the work on the factory floor had no idea of how to use a soldering iron. The one advantage of the clear crimp-on "wire nuts" is that I can see how poor a job was done of joining the wires before crimping. And don't even begin with me about color coding wiring.
In all the trailers I've owned or worked on in the past, not one soldered wire connection was ever found. This is going all the way back to my parent's 1978 Starcraft pop-up. If that was soldered at the factory, it's an industry first.