craftgrrl | Small stencil project help.

Hello all. I've recently purchased a pair of red rubber rain boots with the intent of stenciling them. After browsing around online, I came across a tutorial for cutting stencils ( http://painting.about.com/od/stencillingdecorative/ss/stencil_cutting.htm ) but after getting the materials, I am still having problems pressing down hard enough to do anything but barely scratch at the surface of the plastic material..

I am now looking into trying freezing paper to cut out the stencils which makes a bit more sense since it should follow the form of the boot more naturally. My big question, however, is what can I use to seal my finished work provided I can using acrylic paint for the stenciling? I plan to do two or three coats, each increasing with detail but am not sure if it will run without being protected in some way.

Spray painting is an option I would rather not employee as I enjoy using a paintbrush!

There was also a post "recently" that had a possibly stenciled panda on a pair of white shoes. I can't seem to find that post as I would like to look up the product that poster used for sealing their work.