[LaSwamp]

Wen has a couple of high wattage inverters, but they are not parallel capable for some reason. For inverter power at wattages as high as you need, your options will be limited. Powerhorse makes a 7.5k/6.5k inverter that can parallel as well. On natural gas, you may not get quite up to 12kw though, but you should be able to get fairly close.