Re: Charging house batteries while trailering.
I have three batteries on my boat - two on the original system and added one for just the electronics that are isolated from the rest of the system; the charging system charges all three. I added a solar panel through a split charger; one side to the electronics battery and one side to the original system. The diodes in the split charger prevent 'intermingling' of the systems. The solar panel keeps enough of a 'trickle' on all the batteries to keep them from discharging. Since they are fully charged at the end of each trip, they pretty much stay that way.
If you are not the lead dog the scenery never changes.
1978 21' SeaRay Cuddy
w/260 Mercruiser I/O