hhmmm...I don't recall the sealed bag was the end solution....'cause the pump's gotta pump air to (and from) the latches...the pump needs to suck/push....hence I think the bag idea led to condensation/sweating...which was one water source..
..the other was water used to run down the filler cap yellow pneumatic hose onto/into the unit and..
.. if you didn't/don't keep your rear gutter drains clear (SLKxxx), water may enter the trunk/boot...run down to the trunk floor and then sit and sweat+cause more condensation around the foam box hosing the PSE (the pump unit we are talking about)....etc...etc...

after thought....I just re-read your "not sealed up comment" I get you...