I asked IOTA about AGM, charging and they said that the IOTA is not designed for that.
AGM batteries are good, but probably not really necessary for an RV. Their big advantage is that they won't spill, very usefull in a boat or aircraft, but in an RV you will get the best bang for buck with a good deep cycle wet cell battery. Two 6 volt golf cart batteries are a popular choice. Amp hours are the measure you want to look for, CCA and MCA ratings are for auto, and marine STARTING batteries. (not all "marine" batteries are true deep cycle batteries).