Ron .... a military grade heavy duty alternator is heading in the right direction. Keep in mind to price shop when you do this ... look for HIGH PRICES, not low .... as that is an indicator of quality. Shy away from prices which seem too low - as the alternator most likely won't last - even though appearing to be impressive ... initially.
Now, if you really want to treat your RV batteries correctly ... combine a high output high quality alternator with one of these Sterling products:
http://sterling-power.com/collections/alternator-to-battery-chargers/products/alternator-to-battery-chargers-up-to-400a
