charging from shore power
has ABSOLUTELY NOTHING to do with the alternator wiring path to the batteries
usually when the MFG builds the RV that charge path is secondary consideration
designed to keep the batteries at charge level, rather than supply 30amps continuous duty to power the fridge
it is NOT the same wire as that coming from the iota converter, it comes from the battery isolator circuit under the hood
and instead of being a a short run of number 6, it is a long run of number 8 or 10ga
its not a question of what the alternator is rated at
it is question of what can be delivered while driving down the road, day or night, after the alternator warms up and the internal voltage regulator cuts back on the output voltage and current
you want to run it on electric,
try running the generator burn a little gas, let the iota charge batteries, and use the built in generator to power the fridge, that what it is for
it will work better, and you won't kill the alternator or burn up any wiring, or waste time and effort, trying to re-engineer something
the little extra gasoline used will hardly be noticed the cost is much more effective than what you are considering, and generators love to be used
more die from lack of use problems than over use problems