I agree that if you see condensation, you should remove the plastic, but I am a bit concerned why you are seeing condensation under the plastic.
I have the same plastic under my front sofa and I left it because I slide the storage tubs in an out a bunch and I have not seen any condensation. Keep in mind though in my case the carpet in front of the sofa has the plastic removed which might also help. To add to the mix further, on our Bambi which was carpted throughout most of the coach, that year we owned it, I left the plastic on it and never saw any condensation. Not to say I couldn't have missed it, but I don't recall ever seeing it either.
At any rate, I'd remove it, but also want to understand why the condensation appeared (hot/cold fast temp change, leak, etc).