I'm just in the process of doing this on my new layout. My base is 1/2" QuietBoard over 3/8" plywood (the QB is painted earth brown). I am laying Midwest cork roadbed down by pushing 1/2" 19 gauge brads through it into the QB with a pair of needle nose pliers. The brads push in fairly easily and I can pull up the cork any time I want and reuse it, since it's not glued down. Works really well. BTW, I laid out my track and I'm now putting the cork under it, following the track. Works very well. With the pliers, I can reach between ties and bury the brads so they are not visible. No wetting of the cork either - I did O31 curves with no problem using the split pieces.
Tom