First of all, if you only have 12.5 volts across the battery terminals then the battery is not charged, nor is it being charged by the Converter (charger). You should read around 13.5 VDC across a fully charged battery and as much as 14.5 volts when the charger is running.
The awning slides and interior lights of your travel trailer operate on your coach battery.
So, you need to check that your shore power is connected and that the battery is being charged, and that it has water in it. If these things are OK, then your battery should be charging and things should be functioning.
Make sure that when you are checking these voltages, other than across the battery terminals, that you have a good connection to ground for your meter reading to be right.