Tom, yes you could use mettal, but i might have a cheeper, simpler method for you.
plastic styrene sheets. something around 2mm, cut into the shape you wanted then just use the old heat gun method to make it plyable and shape. it's a bit tricker then foam as it cools REALLY quickly.
best trick i've come up with is sculpt (or in your case foam) up a mock up of the part you want, then basically you can either vacuform or just press down and heatgun it into shape. If you have a hairdryer with a "cool air" setting, it best to have that to help speed up the cool down in shape to avoid wrinkles.
(i'm not one to say alot, i rarely speak period, i'm more lurker then vocal, but when it helps, i speck
if you need more info, toss me a pm tom.