I had a similar problem and it turned out that the manual disconnect switch was bad. Originally I thought the switch was fine because it showed 12volts on both sides, but that was just a surface charge.
Power from the inverter/charger goes through the manual switch and then to the batteries. Consequently, I wasn't getting any 12v power to the coach. I hooked a jumper wire across the posts of the manual switch and "wollah" had power to the coach. A new switch(looked like the factory one)was $50 from Del City electronics.