Another technique for the rear glass is to recess it into the package tray/trunk area. Water jet can be used to cut glass and some places claim they can cut tempered glass.
Laying the stock glass fwd is usually the easiest if you can get away with it:
BTW, "shatter" is an understatement! I'd always heard the old "You can't cut curved glass" rumor and learned quite a long time ago that it was more misinformation spread by self-appointed experts who are actually unwilling to attempt anything remotely close to any projects like all of you are building here.
So I thought to myself, "They were wrong about the curved glass. I've got to make an attempt at the tempered" and if you've watched me cutting glass you already know I use a saw method.
So with goggles on, I took the glass to the table and much like Colonel Robert Gibbon Johnson of Salem, New Jersey - who in 1820 stood on the steps of the County Courthouse publicly eating a basket of tomatoes to prove they were not poisonous as previously thought but later died by pulling the same stunt with, I believe, poison mushrooms - I touched the glass to the spinning blade and BANG! Glass squares everywhere! and I do mean everywhere! <- That is something I should've videoed.