I had the same problem with my 2012 Salem 27RKSS this past weekend.
We were listening to the stereo and had the led lights on in the kitchen.
We ran the generator for the Mrs's shower, made a pot of coffee. When we shut the generator off we lost the radio, the lights and the fridge and the radio
We have the slide out working all the time (because I understand it runs direct line which is most likely why I have 2 white lines coming off the battery and one power red line.
What's interesting is that when I connect one battery cable to a post and touch a second wire to the second post I get no spark at all.
on my panel it says that there is a main breaker which I cannot locate.
I may have to take the trailer in for servicing where as its still under warranty until end September.
Got home and ran power from my garage to the trailer and we have lights, fridge, CO detector, radio.
TV 2018 Ford F250, hauling a 2018 KZ 331 TH 12 Sportster 5th wheel, packing a 2015 CF MOTO 800 U-Force SXS