probably a really really bad idea....but...!

[gordyshreds]

what if on your van, if all the bodywork was clean and dry etc etc you sprayed on a clear lacquer mixed with a metalflake. would this look utter crap of possibly work????

[transitgeoff]

it will just flake off unless you prep the surface

[jamieo]

As transitgeoff said it will just flake off unless you prep the surface, it could look cool depending on what colour your van is now and what colour metalflake your planning on using.

I think you need to give a few more details or even post a couple of pics of your van and some of the colour of metalflake that your thinking of using.

Edit: One idea that you could try before painting your van would be to get an old body panel, paint it the same colour as your van then spray on the metalflake so you can see what it looks like yourself.