If you have the space...you might want to consider using the metal 2x4 studs used in commercial buildings. I made my belly pan that way.
Under belly pan... - Toyota Nation Forum : Toyota Car and Truck Forums
You could try using some Luan board instead of the metal...like I did originally. It's about $10 a sheet and easy to work with. You can eventually make yer template from that or just keep it in place as long as you paint/coat it to keep it from delaminating.
As far as using the metal...you will need to add channels to keep the metal from flexing and give it some added strength. Similar to bead rolling...