No. Enabling the coach batteries won't help by itself, because the 12V cigarette outlet your trickle charger is plugged into only connects to the chassis battery, as you mentioned it was charging it.
If there are any other 12V cigarette lighter outlets back in the coach that you know run off the coach batteries, then enable the battery disconnect, and plug a second trickle charger into one of them. That should charge the coach batteries, if they aren't too far gone.
Or, you could plug your shore power cord into 120VAC and use the converter charger to charge the house batteries, but if your circa 2000 unit has the original converter/charger, it probably isn't a smart charger, and would probably overcharge your coach batteries. Do you know if your converter/charger was ever upgraded with a smart (3 way) charger?
Or as Drew suggested, pull the cover off. Or cut a hole in it big enough to let some sun hit the panel.
