On the Lexan/film/debris debate, I know the rules committee has already voted and the following is just M2c from years of track crew work and fab experience with compound curved acrylic.
Vacuuming up 1/8th" shards of transparent glass shards on a salt surface over miles of track is not practical. From personal experience, it was impractical on dark, hard pavement on a far more limited track! If we couldn't sweep it with a broom, it was left for everyone's vehicle to "displace" in subsequent sessions.
For vacuuming: One, it's too easy to miss things especially in soft salt conditions where the salt debris is thicker than the size of the glass particles. Two, the salt will toast those vacuum motors pretty quick; I'd wonder how long the ones they use last and what the crews (smart, experienced people) hose them with both before and after race week. ACF-50 would be my choice.
JL222 and Bvllercr are right: compound curves in glass, transparent films, or plastics bite the big one. With film it's no big deal, we just add seems and overlaps. With acrylic or Lexan the degree of hassle is proportional to the square of the thickness and the degree of compound. I will post methods for anyone interested. As far as the Firebird and Camaro rear windows go, they're close to flat-wrap: GM is not stupid and compound is more expensive than flat-wrap. If we can wrap film, we can bend Lexan. If we can't, it's a major b---ch. Film inside AND outside would be good along with some specification of type of film and age (see below).
As far as deflection due to pressure goes, to use Lexan at high speeds I'd add LOTS of stiffeners on the inside with nice, big fender washers to the surface and a full frame (like rally cars, good picture there). If it bends, add more. The cockpit is always under more pressure than the air going around it, in aircraft we call this "blowing out" the glass. We have this issue with every new design. It is solved with either decreasing the gauge of the acrylic to the point that it will handle the compound curve during forming or adding supports so that the size of each piece is decreased along with the degree of compound (look at Glasair vs. Lancair). Only one high-performance aircraft in the last 30 years didn't have a full frame on a big canopy (Venture) and everyone with that aircraft changed to a full frame for all of reasons raised on this board by some pretty smart people.
Last note: All, and I mean ALL, elastomers and hydrocarbon polymers (acrylic, Lexan, film, etc.) age due to oxidation with time, altitude, and UV exposure. Some films are more resilient to this (3M), some aren't (bare Lexan, tint film). I'm speaking to the experienced (and therefore, professional) racers here: All of you take a great deal of care (and pride) in your vehicles and safety equipment far beyond the rules requirements. Do the research on the options and make reasoned decisions on window materials, films, and reinforcements within and beyond the rules. As you do now, and have done for years. This is a time vs. money issue: learning more about the subject will enable everyone to fab their own safe solutions at low cost vs. blowing a lot of money on someone else's.
