Most masks aren't capable of filtering gaseous toxins like the volatile solvents found in plasti-dip and PVC cement, or the fumes emitted by melting plastic. They can only mechanically filter out dust particles.
I investigated plasti-dip for similar purposes, and determined that in order to make 1 dart, you'd need to dip once, wait 4 hours for it to set, then dip again, and repeat this process between 10,000 and 20,000 times. I'm sure that if you were clever enough about it to get a good dome shape you could get a well performing dart by doing this every day for 30 years.
edit: Checked out Taers links. Someone appears to have found thicker plasti-dip than what I was using. Still, if you're going to pour rubber into a hole, you'd save yourself a lot of brain damage by using silicone RTV.
Edited by KaneTheMediocre, 26 October 2011 - 02:23 AM.