For G2bG you do not need 99% alcohol as it is't a glue. Good old fashioned soap and water will do the job nicely!
As for a scalp protector then this can lengthen your bond time as it will stop a lot of oil and sweat from breaking up the G2BG bond.
A better option for a scalp protector is a liquid adhesive that you can easily pick up at supermarkets or pharmacies!