The worse thing that can happen is your truck alternator will not be rated high enough for additional batteries.
The rule of thumb is 20AMPS of charge amps per battery with a bunch of reserve left over.
The big problem with trying to use the truck charging system is the truck battery being only inches away from the alternator usually is the driving factor on how much charge the alternator is going to provide for the batteries further down the line.
My number one rule is always leave the truck starting battery system alone and not bother it. Its purpose is to get me home when I need it too.
I would install a good smart-mode converter/charger system for the house batteries and re-charge them with a 2KW Honda generator direct connected the 30A shore power cable using a proper RV30A-15A adapter plugged into the generator 120VAC receptacle....
just my thoughts
Roy Ken
