This is a quick pic of the mold for the 40 Ford sedan delivery.  I taped the windows with masking tape, mounted the master to a base, built a wall around it, poured silicone on top & around it. Took the wall down & had this mold with the master still in it. The second pic shows the "plug" for making 2-piece bodies.

Here's a link to the step by step procedures for this and more of Korkut's tips:

http://groups.yahoo.com/group/modelcarlist/files/tipsindex.html

1) Start by making an impression of the body panel you wish to bash using heavy-duty aluminum foil. It is important that the foil be thick (Korkut recommends .2 mm) because later it will serve as a mold. To make the impression, lay the foil over the body panel and press it onto the surface. A toothpick or cotton swab can be used to push the foil into the body's crevices.

2) After the impression has been made, remove the foil from the model body. Make sure to leave excess foil around the outside edge of the impression.

3) Next, dent the foil until it resembles crinkled, battle-damaged metal. You can go from mild to wild, depending on how much damage you wish to depict on your model. The foil is now ready to serve as a mold.

4) To make the casting, pour resin into the back of the foil mold, manipulating it into all of the areas using a toothpick if necessary. Afterward, allow the resin to cure.

5) Once the resin has cured, peel the foil mold away, and sand off any excess resin. Then cut away the original body panel and glue on your "not-so-new" cast-resin replacement using epoxy or super glue.