Most tutorials on using Instant Mold recommend using Lego blocks to form a box so that the mold does not flatten out too much. The thinner the mold, the more flexible it will be, and thus the more chance that the casting will be deformed.
If you muck it up, don't worry, as all you have to do is drop the blob back into the hot water and try again.
In order to set the mold material quickly I dropped the mold and part into ice water. This allowed me to quickly handle the mold without concern that I was deforming it.
Very easy to make and cast small, complex shapes using this method. As the mold material is reusable, there is no reason to keep molds around after you are done with them. Simply dump them in the hot water and make a different part.
As you can see above, here is one of the assault rifles painted and in the hands of an African soldier featured in the first picture of the last blog entry, for my AK-47 campaign (that I may eventually get to).
I hope you found this little tutorial instructive. I think you may see more use of Instant Mold by me in the future.