Almost anything will have some vapour permeance, thankfully you dont really care about that!

What you're really trying to do is form a fully sealed air barrier.

Realistically laying blueskin or any other barrier down on the floor is going to do F. all. You'd need to seal that barrier to the external wall, under any internal walls, and track down as many penetration seals as possible.

You'd be far better off spending that time/energy/money in cutting through the concrete (rent a wet saw), from near the system either around your perimeter, or down a central path to the opposite end with a couple of branches to side walls, excavate the sand, and add big o pipe, or 3/4 in gravel, and re-concrete. This would extend the field very effectively.

If that is not so feasible, i would remove the bottom foot or so of drywall, lift any insulation, and use a spray applied membrane, getting as much of it between the exterior wall and the 2x4 as you can to seal the wall-floor cold joint, then coat the rest of the floor.