As far as a marquee retainer, What I did for my cab was:
Take a strip of lexan that is the width of your marquee. The strip should be about 3" wide. Clamp it to a your workbench so it overhangs by about 1.5" , Use your butane blowtorch to slowly and evenly heat it up. Use 2 long strips of wood to sandwich and bend the lexan to the desired angle. Wait until it cools and spray paint semi-gloss black.
You can bend one strip to about 120 degrees and another to about 80 degrees for the top and bottom retainers.
Mine ended up looking very professional, and was quite easy to do.
Lexan is easy to heat and bend, The key is to move the torch back and forth over the length of the lexan at a steady rate and heat the lexan evenly. Once the lexan starts to bend down under it's own weight, it's ready to bend.
Hope this helps, I'd like to hear other peoples results trying this.
-PMF