Adwriter, the 55 Iota is more than enough unless you have a huge battery bank. There was some strange applications from Airstream in the past with the old Univolts as they use to call them when they had huge 75 amp units in 31 foot and even smaller trailers I think. I think most of that was because the charge output was less and they didn't used to share the load like they do now. I have disected every, triad, litton, newmark, and a host of other that made the converters for Airstream over the years and I do know that 55 amps is more than adaquate for a 31 foot Airstream or any other coach of that size with a couple of batteries.
You will not have any problem and I can tell you for sure that most people over size their converters. 45-55 amps is all you need for most Airstreams. I'd consider a 60-75 amp unit for a 34 footer with a large bank of batteries.
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