Did you check the voltage at the battery terminals?
It may be that there is a main fuse which has popped, so you have no power within the trailer but the battery actually does have power. I suggest checking the voltage starting at the battery terminals and then working your way "out" from there to the fuse panel under the seat, etc.
A battery stores a lot of energy. It can't just dissipate suddenly without some indication (like an explosion!) However it could run down in a couple of hours under a heavy load like running the fridge
on 12 volt DC. When you say it was working fine, how long prior was that? Minutes? Days?
I'm sure you'll get lots of replies here. Dead batteries and electrical
issues always seem to attract a lot of posts and ideas. Good luck!