Mine have never leaked through the studs, and I use the ones that come with the kits. If yours leak through the studs, then you are tightening them too much to the point the weld is breaking. Get some old inner tube and put it on the frame under the gas tank. This keeps is from moving and helps reduce tank vibrations. Since the inner tube helps keep the tank from sliding around, you don't need to tighten the studs as much. Also, make sure you tighten them evenly.
If you do have a tank that has some small leaks, I would just get some JB weld and smear it around the stud base. Make sure the surface is clean before you do this. After the JB weld dries you can paint it black (or whatever color your tank is) by using some touch up paint.
If you want to get out of using the kit tanks alltogether, I would suggest a barrel style tank that mounts behind the seat.
Here is the tank (4th down): http://phantom-bikes.com/shop/parts/custom-parts/
Here is the tank on a bike: http://phantom-bikes.com/images/bike...detail_380.jpg