Why not just bypass that solenoid and see if you get 12v systems power.
I do not know if the Concept does but many CC coaches have a 300A fuse between the batteries and the inverter in the inverter compartment and another in the battery compartment that have been known to blow.
Check your wiring diagram then locate the fuse block and test the fuse with a volt meter.
http://www.shopwiki.com/_Blue-Sea%C2%AE-Class~T-Fuse%2C-300A?o=562280307&s=155263
I have found them at a solar store also. Much cheaper online. Carry a spare.
Hope this helps.