As this is small scale there are basicly three ways I would recommend depending on what your resources are..
First prototype a shape with all the right dimentions. I like shaping them by hand out of MDF or styrofoam/fiberglass then sanding and filler primer. If needed I would use a bit of body filler to smooth out potential mistakes between sanding and filler primer build up. But this is only if the shape is giving you a hard time. Now go to step 1 or 2..
1. Then you need to make a silicone mold by boxing in the premade prototyped shape and pouring two part silicone. Wait for it to fully set. Then pour crete in the mold, add a strip of steel mesh and wait for it to cure.
2. Lexan can be used as a mold by heating the lexan and using a vaccum box to shape the lexan to the premade prototyped shape. Then pour crete in the mold, add a strip of steel mesh and wait for it to cure.
Third option is skipping the prototyped shape all together and just make a simple wooden box mold so that the inside dimensions of the mold will result in the desired shape with the right angles and what not. Then pour crete in the mold, add a strip of steel mesh and wait for it to cure.
Good luck and have fun!
