Remember that, due to their low internal resistance, AGM batteries accept more charging current at any applied charging voltage.
So .... if you have what you consider a "marginal" charger and/or alternator for camping off road for days at a time .... your setup would be even more marginal in this situation with wet cell batteries. So far after using AGM batteries for years everywhere - including around 8 years of the same set of AGM batteries in our RV - I see no disadvantage to them other than cost.
