Overcast you get no solar, no matter if you have twice the panels.
Mixed sun and cloud days like we often get, you get more AH by having twice the panels for when they get some sun.
One panel that can be pointed at the sun when it is out can have the same sort of benefit. "Depends" whether one tracking will do as well as two not tracking.
Tilted up pointed South is always better whether one or two panels if not tracking.
Although not being in the "PNW" (being in Canada) we do get similar weather. From my experience so far, trying various schemes, we get almost as much with one tracking as two not tracking.
So it might be cost effective, considering the amount of time in those PNW conditions, to make your one panel portable and forget the second panel. That would cover all the bases until you know for sure what the future requirements are.