see the biggest problem with most of your idea is that they only work in 2 dimensions, not 3. the case am planning will have compound curves and such.
as for 3d printing, i am terrible with 3D modeling software first of all, and second, TOO EXPENSIVE! meh ive been up all night and i need sleep now....
calm down, as a 3d artist I can say that palmertech's idea would work fully, he just needs to reword it.
You divide up your case into 4, the top and bottom, the left and right. Make the top left half mold, vacuum form, rotate, do the other quarter. Now this is only with the screen cut out as the button holes would be all screwy. This is also saying the screen hole is in the middle and not more towards the top or bottom. Then do the bottom left, rotate, bottom right. This is also just the basic shape. Then manually make the hole with a drill, sand out the roughness.
If this doesn't work then your portable might be symmetrical but I can't help unless you draw out a blueprint, I could then make a 3d model for you to view, and I can figure out a way of vacuum forming it.