From my expirience you have the same problems from both. I have tinted a few drag car windows in the past that were Lexan (warning them of the potential problems) And saw the same problems after some time. It seemed that the older the lexan was the less problem of bubbling. On my KFIV I am going to install the one piece from LP (Acrylic). What I plan on doing if the heat is unberable is to lay perferated vinyl. You usually see it in the back windows of trucks with designs on them... lots of little holes. Most vinyl shops have it or can get it. There are enough holes in it that gasses should not be a problem. You can still see out but it cuts the light down by about half. Just a thought.

Chris