We used a 1300w heatgun. The board got a little tweaked from some areas getting hotter than others, but you cant tell it with out feeling the board. As for discoloring and bubbling, nah. The Lexan was 1/8" thick .. and took about 10 min to heat up the 34" strip of it. We had it clamped to the table with a 1x1 aluminum tube and some clamps on each side, and then one kid had a large 2x4 to bend the lexan.
Keep in mind, that lexan is flammable after 800 degrees (at least thats what the warning said on the plastic cover) So dont get it too hot .. and practice a few times on a spare piece, because it is a little tricky, and if you've never done it, you might wreck the expensive lexan.
Good luck.
(Edit)
Heres a picture of the setup we used to bend it ..
http://www.eaglerobotics.com/images/...an_bending.JPG