Hi Dan,
Regarding your polycarb question...
If you are only bending the material in one direction, you really wouldn't need to heat form the bend, providing that your means of securing the window will hold the bend in the material.
On real tight radius bends not using heat, it isn't uncommon to have small light fracturing occur over a period of time with flat material held fast into a prescribed bend.
If your bend for the window is going to be curved in two directions, (Like a sphere) heat draping/heat forming must be used.
The problem I see using a heat gun, wanding it back and forth over the material is... You most likely won't be able to heat the entire piece in a uniform way and still reach the prescribed temperature.
What I would do if I needed to heat form polycarb material would be to build a sheetmetal box with a lid, which housed the mold or form.
Add some insulation to the exterior side of the box for easier heating.
Place a simple candy thermometer through an 1/8" hole in one of the sidewalls at or near the elevation of the mold.
Run some flex line or duct into the box and use a heater or maybe even a heat gun would be enough to get the insulated box up to temp.
If the shape of the mold lent itself to a tricky drape, I'd probably drill small holes in the mold and turn it into a vacumme mold, so when the material started to sag it would be held in place and not allowed to fall off of the mold.
Hope this helps... It should be a fun thing to do.
