Your 4x12 is little more than half of our typical 2x20's. A 4x20 is really 2 panels of 2x20 connected. For a 27' AG we use 3 2x20's. A 4th would warm things up quicker, but for now we'll stick with the space/cost of the 3. They only lasted 2 years and got many leaks so now we're stuck replacing them, but it's still cheaper than a gas unit. Plus in WI I imagine our nights get cooler.