Been there myself. Blown fuses always = short circuit. You have rubbed the insulation off a "hot" wire, probably where it crosses the axle. When the raw (exposed) wire touches the frame (when you go bump) the fuse blows.
You can pay somneone to do repairs of you can pull new wires a lot cheaper. I like to pull an extra white wire along with the others to get the ground above the trailer frame. My last wiring job this way lasted 26 years trouble free.
Heck, I'll even help you pull the new wires for free, if you like.