Depends on the kind of dash you are working with... I know that you can glass something to a metal dashboard much the same way as any other bit of bodywork (kind of like firberglassing a hood scoop onto a hood using a fiberglass mat and resin). The same thing can be done with plastic dashbaords like the mid 70's and newer GM's as long as the surface you are mounting to is scuffed up first. I doubt that you could do that to a vinyl covered dash though.
Here's a thought, you could also use screws hidden on the inside of the enclosure to secure it to a dashboard and hide the edges with another line from another feature on the dash.