Iota (as mentioned by Robert Cross) and Progressive Dynamics "Inteli-Power" are widely used and praised in the Airstream community. It's probably not a problem if you order from BestConverter, but if you search Amazon or eBay be sure to get a model that has 3-stage charging.
I use a Powermax Boondocker in my trailers (also from BestConverter) and have been entirely satisfied with those.
Whichever one you choose, it'll be smaller, lighter, quieter and better than the OEM battery-boiler, especially if you're full-timing.
Il Carriaggio — 1975 Argosy 24 | Il Progetto — 1976 Argosy 28 Center Bath | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. — Sir Winston Churchill