Wait...
SOG, describe to me again how you are setting up the floor...
plywood then rubber than panda film?
If anything, I would do as Lions and have the rubber ON TOP of the plastic...
But even then...
Moisture can still get trapped under the rubber, inviting mold and millions of spores into your grow...
I am not sure what I think is best here, but I am starting to think that bare floor is the answer...
Any seam or joint will allow moisture through..
Even the panda film is not perfect, it has holes on it where it was folded... small ones, very tiny, but water is also very small...
The only real way I see, is to have something that is 100% seamless
Like on of these car mats, with an edge/damn all around it... but of course the size of your growspace...
That way, water can spill and evaporate, instead of getting trapped...
I am sorry to keep on this subject, but I am just trying to be the Devil's advocate here...