have it done pro (IMHO)... glass can stay in.  I spent $200 for a very nice
metal film here in Hawaii... might be cheaper where you live.  you don't
have to go all that dark if you go with a reflective metal based film.
Makes a huge difference with not only light, but heat in the bus as well.
Good luck.

Mick Kalber
89 Syncro Westy "Daddeo"
Tropical Visions Video, Inc.
62 Halaulani Place
Hilo, Hawaii 96720
808-935-5557
808-935-0066 (fax)
hotlava@interpac.net
www.volcanoscapes.com