Enclosing/casing electronics
The polymer clay (Fimo) is probably not a good idea as it may contain compounds harmful to the electronics and the baking temperature may be too high.

If it's just a few resistors on a board, I often just use shrinkwrap as you do. Otherwise you can encase them in potting epoxy. This is designed to be safe for electronics and just about any kind of enclosure can be used as a potting form.