If it were a new truck you’d probably be ok. There’s two factors to deal with now. The one you brought up about increasing the charge capacity and now the pathway from the charging system to the RV battery.
Yes on the upgrade to the alternator. You’ll want that to xtra charging capacity right up front after potential low capacity starts. It’ll get the truck battery charged back up faster so a short drive won’t leave you with low battery again.
With the increase in load to the lithium battery charging you’ll also want a new set +\- battery cables. These trucks are known to have them last 8-12 years before they build up resistance and cause fake DTC to appear.
