Cardboard might be better, IMO, because it will match the thickness of the material you intend to use a bit better.
A little tip that I have used in the past.
When you get to the tighter curved areas and you realize you have taken too much leaving a gap, take a smaller piece and make it fit the curve, hold it over the piece you took too much off of, while in place on the tray, and trace the inside cut to the larger piece.
Remove the piece by cutting on the traced line and tape the smaller piece in place. This will keep you sane, and you won't be starting over 50 times.
I hope this makes sense.