I'll tell you how I do it... once I have it cut to
size using the glass as a template (use the inside
of the glass for the template) I file the edges nice
then heat the edges with a propane torch to give it
a clear edge again... I like to paint the perimeter
with black paint... tape off the area not to be painted
then use a fine paper or scotch brite then paint...
I attach it with screws... place the glass in place
and hold it with tape... drill a pilot hole through
the plastic and the metal spacing them evenly... pull
the glass and drill a clearance hole in the plastic
for the screws you will use.... clean the holes and
clean the glass... install a rubber/foam gasket and
install the glass
NOTE
when you use a torch to clear the edge start on a
scrap piece to get use to how much heat to use...
the heat will give you a radius also to give a
finished look