I have not done a double thickness kilt - yet - but I have been making garments/costumes for a long time and it is an easy option to double a fabric in order to get the weight of older cloth without the danger of a heavy interlining making what should be a fluid fabric look wrong.

You might need to put in some lines of basting thread to help you to keep the layers from slipping on eachother during construction, or just sew through both layers at intervals, where it will not show. Thats is the only problem I could see with a poly cotton. It might help to fold the pleats and press them in using strips of card before starting to sew