I would be thinking sufating.
I am far more familiar with FLA but I do understand that AGM are subject to sulfating just like FLA.
With FLA you want to charge at around 10% of C20. AGMs will handle a higher rate of charge than FLA.
If you don't charge aggressively the plates can sulfate reducing battery capacity. I would look at having at least enough solar to be able to charge at 40 amps. Taking into account the fact that you are unlikely to ever see much over 70% of nameplate ratings from your panels. 800 watts of panels will get you in the ballpark.
Anything less can reduce the lifespan of your batteries significantly.
There is a solar forum with some really sharp mods and members when it comes to solar. Http://www.solarpaneltalk.com
I have found that RV specific knowledge is a bit weak but I have not found a better source of quality solar and battery information. Take a look at the stickies in the battery section. They are quite an education.
Good luck.
