Using an alternator to feed your house batteries?

Since the house batteries are one alternator, the chassis on another, they have no contact with each other. I plan to keep them this way, just so an electrical fault with the RV part won't affect the engine or drivetrain.

Catastrophic fuses go without saying. I like having those on all the main paths, just so that a short doesn't mean a swath of pure destruction.

00 wire makes sense, I was even thinking of 000 wire, just so voltage losses are minimized.

As for load, at idle, the secondary alternator sits at 160 amperes, so it isn't too much drag. It is present, but it isn't anything out of spec for the engine.

This is for a custom class "B" motorhome, and 500 watts of solar will be difficult to place on the rig, unless I go with a portable solar rig, which I don't really have room for.

What is wrong with the system now?

I would be more inclined to put 500 watts of solar on the roof. Will still charge on the road but more importantly the battery will tend to stay at a higher charge level before you even roll.

The theory sounds workable to me, in general. I might think about rejiggering the battery isolator system so that the house and chassis batteries are not tied together while the engine is running, though that's probably not essential. I'd also make sure that the new alternator is rated for continuous heavy-duty use; many are really only designed for intermittent heavy loading, and that's not what you're proposing.

Do make certain the regulator sense wires are connected to the batteries that the respective alternator outputs are going to. It would not be good to have the alternator sensing the chassis voltage while powering the house system.

"Proper wire gauge" is going to be quite heavy.

sure you can
your going to need multiple strands of "2 aught" cable or maybe something larger
unless you fuse the cables near the alternator, for the max rating, of the smaller cable run

issue number one will be power you rob from the engine to drive this humongous load your thinking about, the strain on the belts and the additional load the engine cooling system and pulleys

nothing that can't be solved, IF you throw enough money into all the heavy duty OTR parts needed for the job