Picked up this incomplete 32 Chevy made by Hubley!Missing the trunk lid so I thought I would cut a piece of sheet styrene slightly over size and clamp it to form the correct curvature.The plan is to immerse it in boiling water and allow it to cool. 
I’ve used that method a few times. One suggestion, on the ends where the piece is clamped, put a piece of wood or metal between the clamps so the piece is held flat all the way across. If not, you might end up with bulges where the clamps are. I’ve had that happen.
Good luck.
Jim [cptn]
Ok thanks for the info!
Ok it appears to have worked,dunked it into the boiling water for a 20 count.Glued the rumble seat to ensure it retains its shape! 
Came out pretty well! 