I was down under my trailer today, greasing the guide bar, which has remained completely rust free in spite of my neglect, when I noticed another thing that you should look at under your trailers.
My electrical wiring to my trailer brakes is routed from the tongue to the curb side wheel. There it was connected, using indoor wire nuts to the wires for those brakes and to the wires that run across the underside of the trailer to the street side brakes. Again, these wires were connected to the brake wires using those indoor wire nuts. So, there's two things to check on here, and possibly correct:
1. I think the wire nuts should be replaced with something that is suitable for outdoor wet locations. There are automotive connectors that satisfy this spec and I've replaced my wire nuts with these (available at automotive stores).
2. The wiring that runs across the trailer from the curb side to the street side may not be secured properly and may be "hanging down". Mine was hanging completely free and was drooping so low it could easily catch on anything sticking up in the center of the road. The solution here is simple, just tie that wiring up to the frame cross member above it with zip ties. There are already holes in that frame, making this modification easy.