Dead Battery? No lights working

Hi there. I have a 2003 Cougar Fifth Wheel. I was using a space heater and it kicked out my breaker. I reset the breaker box outside, I reset the breaker panel in my fifth wheel. I reset the GFI. However, I'm still having no power from the batteries or 12V system. All my power outlets work, but most of my interior lights don't work, the fridge has no power, my level reader has no power. What can I do to fix this? What else do I need to reset, and how do I do it? Please help! Thank you!