hey, I didn't think to do that in my stress test... I did use the score-and-crack method on the long sides though, and a single punch down on the scrap side left a nice clean crack.
I tried nails, table saw with no supporting wood, circular saw, and drilling wood screws through too-small holes, and it all produced good results except the nails. I did get a couple long lexan fragments stuck horizontally in the table saw though, and they spun around repeatedly smacking against the saw guard.
As for your trapezoid shaped marquee space, do you have your lexan sliding into a routed slot? if so, just make the slot a bit deeper in certain places. If not, a table saw will trim lexan to precise measurements. I don't know if I'd try a circular saw, it's too easy to mess up and take too much off. The router and clamped straightedge method Rebirth suggested may be your best bet. Have a friend with a vacuum cleaner follow your router bit while you cut, it might cut down on the mess.