Mine were about 36" long. I place them on a block of wood at each end then used hot water and towels to keep the heat on. set a weight in the middle till you get a bend about the same as the curve you need. When it cools down the curve will hold. Then I used a couple of U bolts to clamp a long 2x4 between two stanchions and cut short pieces to go from 2x4 to window. I used one at each end and one in the middle. Once I had all that the right size / length I put the sealant on and let it sit over night. Worked perfectly. I used the dow corning stuff, 795 I think.
Brian