I use 95% infill, but I don't know if that's totally necessary. I do that due to the stress placed on this. I've been printing in PLA, but ABS would be better. One if my friends had his PLA fender deform when sitting in a hot car. I've left my ABS fenders in cars and they have not yet deformed.
You will need supports on the fenders with designs in them. The basic fender does not need any supports.
I print directly on Glass. I will sometimes add glue stick just so it does not have a chance to come off. It's about a 6-8hr print.
I do not use a raft, but that's up to you.