Thanks, Jim. That little window shaker looks just the ticket of what I need.
As it is, the extra 2" of foam board I installed in the ceiling cavities does a great job. If I let natural or fan-aided night time circulation fill the trailer and close windows in the morning, the interior stays cool until well into the afternoon. This is when parked in full sun with daytime temps into the 90's.
Still, an additional panel and two more batteries will get me off-grid AC (for a period) and that would be a welcome addition when on the road.