Right after a 5 hour trip I would expect to see the house batteries reading about 13.5 volts or so, dropping to 12.6 volts after a load had been placed on them for a while.
Note that The AUX solenoid and the and the disconnect solenoid are two different solenoids. I mention that because you said 'AUX disconnect" above.
I would start the engine and see if you are reading 14.5volts or so on them. If not then the Aux solenoid is not being activated or is not working.
The AUX solenoid is activated in two ways.
1) By a wire from the RUN terminal on the ignition switch.
2) By the AUX switch on the dash.
I have a Workhorse chassis and on mine there is a fuse in the fuse panel under the lift up dash labeled "Step Warning or Step Alarm" I don't remember which.
It is on the far right row of fuses and is the top fuse. As I recall it is a 15 amp fuse.
One side of the fuse goes to the RUN terminal of the ignition switch the other side of the line from that fuse goes to the rear heater fan, the back up monitor, the AUX solenoid and the steps control board. The step control board tells the steps to retract when the ignition is on.
I had to replace my AUX solenoid last April and it was real bear to get to. See my thread HERE