I'm still not ready to post a tut, but I've found a really good method that I think will work on a consistent basis.
Vinyl or contact paper itself is too thin to stop the running of the gallery glass paint. So, I've come across the idea of applying the vinyl/contact paper to the transparency (or other plastic - whatever you have on hand), and on top of that, going over the lines of the vinyl with a dimensional paint like SU's crystal effects. The point of doing that is to create a "wall" that will stop the running of the gallery glass paint when you apply it. You could use glossy accents for the same purpose. As much as I love glossy accents, for this purpose, I much prefer SU's crystal effects, because it doesn't run (it stays put for the most part), and I find I have more control over the applicator tip with the SU product. Your mileage will vary, so whatever you prefer. This is also known as a "reverse" painting technique for those of you wishing to investigate.
I still have to finish my explosion box, and I still have a few up in the air projects. But I have not forgotten about doing a tut. I like to make sure that I can get repeatable results before doing a tut.
Pat