Why use plastic? It is very soft, will get brittle and discolor
in time and the adhesives in tape might cause a problem.
When I built my light box a few months ago, I went to the local
glass and screen place, the phone book was full of them and
asked for a two foot square section of "frosted" or "ground"
glass. It was ready in three hours and cost 36 dollars or
nine dollars a square foot!.
The frosted glass sits over a well constructed in the bench top to
give a flush finish. All the mesh points are sanded or caulked to
give a snag free surface. Total cost was thirty six dollars for the
ground glass, twenty for the two foot, two bulb fixture and five
each for the bulbs. The wiring and switch were previously in place
from the original darkroom construction work. The well is two feet
deep and thirty inches wide, painted on the inside wth WalMart's
best exterior siding and trim paint, gloss white at ten dollars a
gallon. The switch was 39 cents and probably fifty cents workth of
wiring.
Hope this helps...
Howard Etkind