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?