The RC7-GS inverter charger can properly charge 105Ah AGM batteries using the 125Ah setting, as AGM charging is voltage-based, not capacity-dependent. Generator start issues typically stem from wiring problems or incorrect DIP switch configurations.
Your East Penn 6V AGM batteries likely sustained some damage from the complete discharge to 8V, but your charging behavior suggests they may have recovered reasonably well. The key indicators are how they hold voltage under load and their actual capacity.
RV batteries draining overnight typically indicate a parasitic drain from components staying powered when they shouldn't. Use a multimeter to test each circuit systematically, starting with the main disconnect and working through individual fuses to isolate the problem circuit.
Jayco builds cabinets in-house, but many independent shops in Elkhart-Middlebury specialize in RV woodwork. Search locally for RV cabinet shops, ask dealership service departments for referrals, or contact Jayco parts department for supplier info.
Check internal DC fuse first - common failure point. Located inside inverter behind front panel. Also verify battery voltage at inverter terminals and check MATE controller cable. No display with fan running often indicates blown DC fuse or control board failure.