Vinyl plank flooring on concrete - vapor barrier or not?

I'm replacing some carpet with "luxury vinyl plank flooring" (at $2.99/sqft from Menards, I'm surprised it's not marked "extra luxury" :D).

The "installation instructions" are very limited. It does say it's 100% waterproof, though, and has a "built in pad".

Is it common practice to install a vapor barrier under LVT when installed directly on concrete? The instructions don't call for it, but my concern is that the slab seems fairly damp, and while the carpet probably let a lot of moisture dissipate, will the LVT trap it? In that case, I'm not sure it's any more preferable to trap the moisture under a vapor barrier...

One of the tests you can do to check for moisture coming from or through concrete is to tape a square of visquene to the concrete, wait a couple of days and see if you get moisture under the plastic. This might help you decide is the vapor barrier is needed.

How old is the concrete and what is your climate? If rainfall is under 10 inches no problems, above that I would lay in plastic since it is so cheap.
Bill D.

I wouldn't take a chance with this. Plastic sheets are chip and will provide peace of mind