First of all, the fuses for each circuit that they protect, are designed to blow rather than have anything melt, or worse.
Some RV owners will have problems and place larger value fuses in the fuse panel than are allowed. The result is what you have, a melted fuse holder.
So, the first thing you need to do is try to find out what the original fuse value was supposed to be.
Then you obviously need to repair the fuse holder and the wire.
Once your fuse system is back to normal, then you can chase down what, in your lighting system is blowing the fuse. Possibly a lamp that is the wrong type?