I am sharing my experience when I decided to upgrade my existing (2) 12 volt
Interstate SRM-24 batteries. I have a dealer installed roof solar panel. While I could go 2 to 3 days dry camping, the batteries would fall below 50% at the end of that period. The batteries were inadequate. I decided to upgrade based on a YouTube video at Loloho.com. I started by quest.
I contacted both Airstream dealers in Southern California who litteraly shined me on. I didn’t event get a call back!! I found a local guy in Ventura to change the batteries and install a temperature module. I bought the batteries from Powersource. I did the research re settings, equipment and set up as described below.
I decided to use the Lifeline 6 Volt GPL-4CT. It fits the 12 inch battery box with a slight cut in the plastic battery tray. Airstreams prior to 2015 need an extender as it has a shorted box. I was told the Converter was a single stage type and I needed to get a new three stage unit for the AGM battery. Airstream customer service was very helpful. They said the forum posts maligning the Parallax converter were unwarranted. I contacted Parallax directly. They were VERY helpful. To my surprise, my 2017 already had a three stage converter/charger. I am not sure what year Airstream changed to the new units. They recommended adding a TempAssure Module. I did. Easy install. The solar controller made by Atkinson Electronics works with AGM batteries. They were also very helpful. I actually spoke to an engineer who walked me thru steps for clipping a jumper based on the battery manufacturer specs.
So, I am up and running. I made a lot of calls. Airstream, Parallax and Atkinson should be congratulated for excellent customer service. Lifeline also responded to an inquiry quickly. I was very disappointed with the Airstream Dealers.