re: "if you have solar panels, the lower internal resistance of AGM batteries may be worth the extra cost." -- this doesn't make sense to me. Since the power available from any RV solar system is relatively small, you won't get near approaching bulk charge current limits in any real sense with any type of battery.
As for type, the choice is between AGM, wet cell, and Gel. AGM tends to cost about twice as much, may last 1.5 times as long, and, as a sealed battery, needs care not to overcharge. Gel is better for float service and isn't considered a good battery type for RV's. Wet cell is usually the most cost effective option.
As for labels, like "Marine/RV" or "deep cycle" -- these only tell you the intended market. They mean little or nothing of any significance as far as performance in an RV is concerned.
Get batteries from a retailer who sells a lot to folks like you and will stand behind what he sells. Use warranty, specifications, and cost to guide your purchase. Watch out for those peddling marketing hype that doesn't have pertinent objective measure or clear definition.
The best thing you have going for your batteries is that 9260. Be sure to keep it plugged in and maintaining your batteries between trips.