The thingie would work especially as it would permit the use of soap. Salts will be mixed with dirt and unless you get the dirt off, the salts will remain. There are thingies that attach to garden hoses and ones that are without. We bought a cheapo plastic one—perhaps at Camping World—and it started to fall apart after a few uses at the movable joints at the end parts. I fixed it with a drill and nuts and bolts, so it'll last a while longer. I'd suggest getting better quality than I did.
There are small power washers available that don't have much pressure and that maybe an alternative. However, I'm unsure how long they last. The medium size Delta one I bought several years ago—I think it's 2,700 psi—was poorly made. They replaced the wand on warranty; I replaced the junky hose. Eventually I'll get another brand wand. Anyway I would never direct 2,700 psi on any part of the trailer—it's not like a car or truck. I crank it down a lot or use a garden hose.
The suggestion about using cold water makes sense—hot water dissolves salt crystals into a solution that can be driven into things where the crystals wouldn't fit.
And, salts live on all year, I think. The crystals get ground into the pavement and the spray gets into the dirt alongside the road. When it rains the salt solution comes back like a zombie to attack. When the road gets wet, note the white solution on the pavement for a while. They use a lot of mag chloride here in Colorado; I don't know whether the rock salt used in the NE acts the same way, but I would think salt is salt. There is no escape.