[Richard]

If you want the simple version.

Do NOT even think of charging the lithiums directly with the alternator. Unless you are fond of buying new alternators.
Install a B2B charger to trickle charge the chassis battery from the lithiums. Victron makes good stuff.
There are devices available to charge the lithiums from the alternator; they basically limit the time the alternator is on.
You will need to custom program the Magnum to fit the lithium needs and your intended use.

There are hundreds of threads on the RV forums about lithiums. The above fundamentals will give you a starting point as you dig in.