no power

Is the battery disconnect switch in the correct position?

Our 12 volt system died in the dealers driveway and it was the circuit breaker that was hidden under the rig for the main cable coming out of the battery. It was originally a manual reset (believe it or not) but they changed it to auto reset. I never knew it even existed until the problem.

If your lead acid battery got discharged to nearly nothing and sat dead for a short time it probably sulfated and will never hold a charge again.

Had it happen several times and it was always a fuse or low battery.

How long was it sitting since you last plugged it in?
There are phantom loads like the CO/natural gas detector, the control board on the fridge, the radio, etc that drain power every day. You probably drained your battery so low that you damaged it, and an overnight charge likely did not restore more than a surface charge to the battery. Grab a new battery and test, if it works then you've learned a costly, but not very expensive lesson. If you'll be continuing to store the trailer away from power you can protect the battery by adding a cutoff switch, or by adding a solar panel (trickle charger would probably be sufficient, but for not a lot more you can add a 100-150W panel that will also allow you to do some boondocking, and isn't going to walk off like a trickle charger panel might).

Sounds like you possibly forgot to disconnect the battery while in storage. This can drain the battery in 1-2 weeks due to Phantom loads. Once you charged the battery it's possible you connected it in reverse and blew the reverse polarity fuses on the power center. Depending on the model the fuses might be on the front of the panel with the rest of the fuses. Some models you have to pull the fuse panel out to access the reverse polarity fuses on the back.

Do you know if you have 12 volt or 6 volt batteries, it makes a difference. Check that the battery wiring is correct first. If you have a multimeter check that you have at least 12 volts at the battery. 12.6 would be best, but make sure you at least 12 volts for the lights to work.

After verifying the wiring check the positive wire between the battery and the trailer looking for any fuses or circuit breakers. Use your meter to verify that you are getting the same voltage on both the upstream and downstream sides of whatever you find.

Go into the trailer and open the fuse panel. Use your meter to check each fuse for power. Do you have power at the panel?

Multimeter time.

Set it to DC voltage and starting at the battery work thru the system until you don't get voltage.

Lights should come on even if the battery is low (they may be dimly lit), so I presume there is a break in the circuit somewhere.

Assuming the battery charge took (ie: battery isn't totally shot which is unlikely but check it first) and no 12v items work, my first guess would be a connection to the battery is loose or disconnected. After that try pulling fuses to see if they are burnt out (check the voltage across the fuse terminals when they are removed also).