OK, this helps.
Before we go digging into the junction box on the front of the camper, lets try this to get the 12 VDC up and working.
Something is really not right if there is no 12 volts working even from the battery. The microwave panel should of at least lite up from the 120volts being on but will get to that after.
Lets try this. First, make sure the camper is dried out and there is no visible water on OR in the power converter. If you find any along the way, then stop! until it dries out
You said you checked all the fuses at the converter panel right? Yes/No?
Unplug the 120 VAC shower power. We can trouble shoot the 12 VDC side with it off at this point.
Set up your volt meter for DC volts. Check the battery voltage at the battery posts. If it is a digital meter, tell us the exact volts including the decimal point. Turn on the battery disconnect switch.
Next is at the power converter. If this is too much to do for your ability, stop and you will need to get a electrically friendly buddy to help.
This procedure below assumes you have a basic working knowledge of 12 and 120 volt electricity and can take the necessary pre-cautions to be safe.
Take the face of the converter off.
The 2 silver head screws in this pic hold it on.
When the cover comes off it looks like this
Then put your meter on DC volts and place the meter test red lead on the big heavy red wire on the top of the fuse panel. The big red wire with the hex bolt in it and the 2 black wires also bolted to it. This is the battery hot wire
And place the meter black test lead on the large white wire with the hex bolt on the bottom of fuse panel. This is the battery ground, negative wire.
That big red and the big white are the 2 battery lead wires. If you have DC voltage at the battery, it should show up at the converter panel on those 2 wires. If it does not,
then there is an issue out in the junction box on the front of the camper. Will get to that after if it is.
If you do have voltage
at those big wires, then we need to go to the next step and figure out why the power is not getting to the fuses.
There is 2 big green 30 amp fuses on the top of the fuse panel. Pull them out and make sure they are not blown. If you had a short from the water, the would blow them quick. And if either of them are blown, that will now allow the DC volts to pass to anything in the camper. They are the 2 main DC fuses.
If the fuses are good, then the socket has some issues. With the fuse out you can test for voltage with the meter. Use the large white wire for DC neg and the fuse socket for the red test meter lead. You should get volts there if you had it at the big read wire. This is what the back of the fuse panel looks like. Just blades of metal.
Do not pull the fuse panel cover off with the battery still on.
There is the capability of high current if you cross the + and -.
This should turn up something that is or is not working on where to go next.
Hope this helps