AGM batteries can be discharged down to 20% compared to 50% for flooded deep cycle. So I would say the battery lady doesn't really know what she is talking about.
At the 20 hr discharge rate a pair of Group 31 = 210 AH and a pair of GC2 = 190 AH. So I would go with the Group 31.
2007 Surveyor SV230 - 200 Watts Solar/MPPT Controller - 230 AH Battery Bank - 600 watt PSW Inverter - (2) 2000 watt Inverter Generators - LED Lighting
2009 F150 - 5.4 Litre - Tow Package
Boon Docking 99% of the time.