Welcome to the Forums, and to vintage trailer ownership.
So just a few words in advance--if this trailer is in its "original" condition, that is to say, that nobody has spent thousands of dollars to reverse the 45 years that have passed since it was built, then hold onto your hat, because you will find that the only thing on these trailers that seems to last forever is the shiny aluminum shell. Manage your expectations--and expect to do some work making this trailer safe and functional.
Now to the electrical: Did everything work before you had the positive terminal incident with the battery? I would guess that it did not. If you think about circuits, you have your positive and negative terminals on the battery both hooked up, and then the positive termal comes in contact with the shell. The "short circuit" you just created is going to go from the positive terminal, through the very short section of shell, and then into your grounded negative terminal. All of those DC components in the trailer should be out of the "short" circuit as the electricity is going to take the shortest path of least resistance.
You should have a very simple fuse panel in the vicinity of the battery and converter, and that is it for panels unless a previous owner retrofitted something. There might be an in-line fuse in the wiring immediately behind your stereo (but I don't recall one on my '73), but there are no inline fuses in your lights.
The switches next to the door probably operate the porch light, if equipped. Switches above the sink likely to be for the galley roof locker (cabinet), and the light over the sink. Again, this will depend upone any mods the previous owner may have made.