Caring for GC2s requires using an hydrometer fairly often, so you have to haul them out anyway. It is more than just making sure they are topped up.
AGMs means you need an ammeter to tell when they are full on a recharge tapered down to 0.5a per 100AH at 14.4ish (whatever their charging spec is--some have spec at 14.8) before you drop to 13.x Float. I use the Trimetric for that. Best to have an adjustable voltage charger to manage that.
You will want the performance of 12v AGMs vs GC2s for high amp draws using an inverter with only two batteries.
Deep cycle AGMs come in various sizes, but 27 is one. Can you get two in there?
If you keep the TC on saw horses at home to free the truck, you can do the batteries- in- the- truck bed trick, which allows you to get at the batteries.
