yes it will work - done it in the blue marlin build.
Just make absolutely sure your tank is sealed properly from the inside of the hull, and, as Rob says, you need an air vent. Run a silicone tube from the top of the tank to some discrete point above deck level.
For each litre of water ballast you use, you can remove 1kg of lead.
For best results and minimum effect on stability, keep the tanks low and evenly positioned around the center line of the hull. Also, when building the tanks, put in some wash plates - dividing walls with holes in, this will reduce the free surface effect of the water and reduce roll induced by the ballast water. Remember to leave openings at the bottom of the wash plates for full drainage, and at the top for air venting.
Ian