1/72 Do 24T RLM pain....t....

You should be able to get hard edged camo using Tamiya tape. Just don't spray on your top coats too heavy, and make sure you burnish down the edges of the tape. Thin coats of paint and multiple layers is the key. 

As Nathan said, you should be able to get the hard edge useing Tamiya tape. This is my Italeri Do 24 i finished a couple of months ago, all masked with tape.

If bleeding under the edges of the tape is a problem, you can seal the edges.

When you are done with the lighter color, put one more thin coat down. Concentrate on the tape edge areas, just blend in so you do not need to do big open areas. Any bleeds of the lighter color will be the same color as what is there, so it will not show.  This is a good idea any time you are masking a multi-color finish.

Also make sure you are not spraying "into" the taped line.  You want to spray along or preferably away from the tape.  Spraying into the taped line makes the paint bleed under much easier.  You can also get a bleed if you are too close and the paint is a bit to thin.

Practice on some scrap styrene and pretty soon it will all come together:)

John