I completely agree with the posts about only needing a small inverter for the current usage. But from another angle, the OP is contemplating an upgrade including adding 2x6V batteries and solar. So who knows what they will decide they would like to do with that power once it is available to them. You can afford to be a little less stingy with your 12V power when you are harvesting free power from the sky to recharge. I say go ahead and plan and build around a 1500 watt inverter which is about the max power that 2x6V could run.
