The walls are, indeed, a "laminate", however they are pressure glued up. The outside wall, itself a "laminate" of filon and luan, is laid down with glue, then the aluminum wall is applied, foam blocking installed and then the inside luan, again with glue, is laid down and the entire assembly then pressure rolled to provide the finished wall... At any point, the process may not apply enough pressure or there may be voids that are not filled due to variances in manufacturing; either the foam may not be a uniform thickness or the aluminum framing could be tweaked a bit, any number of variables, but, there exists the possibility that there are interconnected voids that would allow water from a leaking window frame to travel inside the wall to any low point exit at floor level.
Water can do mysterious things...particularly if under pressure as in a driving rain or traveling down the highway. I knew a fellow one time that worked with fluid dynamics. He designed and produced a window washer nozzle (for automotive use) that sprayed an "S" shaped pattern out of what appeared to be a standard black plastic block (the kind that you see on all automobiles). The inside was a complicated pattern of shapes, but, there were no moving parts and the gist of it was that water can take a "spin" and behave with resulting strange exit behaviour, in this case it sprayed an "S" pattern instead of a stream. The nozzles are licensed to Ford (Lincoln) and Mercedes-Benz for their high end cars. Ask any RV shop about strange leak behaviour...how a leak in the front corner can result in rot behind a mid mounted refrigerator...
While it may not be likely, all I'm saying is you can't rule out the odd-ball. If the obvious isn't the problem, it may be the unlikely that is causing the issue.
My 2 cents, your mileage may vary...
2 Cats; J-Lo and Ragamuffin :R
2014 Thor Tuscany 40RX DP
2011 Ram 2500 Longhorn CTD HO
2011 Keystone Cougar 318SAB (now gone)
2008 FunFinder X 210WBS (Sadly gone)