My golf recently had this problem when one of the rubber bungs gave out.
Like said, removed carpet, underfloor, insulation (naff sand blocks) and even footwell sound deadening all soaked through.
I had them on a boiler drying out and used a heat gun and a outside floor standing spotlight but even now with it all back in the carpet is still slightly damp to feel.
Real pain, best bet is to remove all and just drive it with just the seat in until you've dried it properly otherwise it'll never seem to dry up.