Fender Flares

I have after market fender flares on now and would like to add the extended fender flares. I have seen where people take mud flaps from 18 wheelers and cut them to fit on the fender flares. I just have a few questions. How wide did you cut them? How did you mount them? How well did they hold up?
I cant justify spending $100 on the aftermarket set when I can get the mud flaps free. I have a set that are 36"x24" and 32"x24". Hopefully I can use them.
Just looking for the best way to do it. I have seen pics on here before but I cant seem to find them now. Any advise or pics would be great.