Black garbage bags will not work. Even the heavy black polyethylene used for construction is not light tight unless you use several layers. Ask me how I know.
It is relatively easy to remove curl but you have to be gentle. On a smooth surface; place the paper emulsion side down and place a rigid straight edge close to one edge. Hold the straight edge and pull the paper up against the straight edge letting the paper slide underneath. If you are not careful you can get pressure marks which will develop as fogged areas. I used to do this to 50" paper when necessary.