How to Make a Belly Cast

Supplies needed:
Rigid Wrap. (http://www.michaels.com/art/online/displayProductPage?productNum=gc0027) You can buy this at most craft stores. I would buy 3 packs, maybe 4. They should cost about $4 a pack.
Vasaline.
Old bra
scissors
bowl of warm water

Directions:
Wear the old bra. Wear grubby pants down low under your belly.
Slather your belly and breasts with the Vaseline. Make sure you cover every area you plan on casting. This will allow the cast to come off easily.
Cut the rigid wrap into smaller pieces. Some about 8 inches, some 12 inches, some 18 inches.
Dip the larger pieces in the warm water and lay on your belly. Smooth it out.
Do that all over and in different directions. Smothing as you go. Use smaller pieces in touch up areas.
Do a few layers.
Try to make a nice edge.
It will harden quickly and you can lift it off.
Shower off and wash all the Vaseline off.

I've also heard of women using plastic wrap (like saran wrap) instead of Vaseline. I've never done that.

I hope it works for you.