I am laying down some laminate wood floor this week in my house over some older wood plank flooring. I was just going to put roofing paper down and then some foam style underlayment Home Depot recommended. The issue is the floor, being old planks, is not very level spanning the room. The corners are pretty low, maybe 1/4" dip. Should I lay down some liquid floor leveler on this floor or just build up the underlayment to make it more level?