Ive never used prep h method but Ive used a wrap before. For me it lasted for like an hour after wearing it for about 12. I liked to take it off about 30 minutes before the taping to get ride of some of the lines and make it seem more natural. I dont think it would matter if they saw huge red lines or light ones they would know you did something.
I could only assume they can smell it. I dont recall anything being in the regs about it but they keep changing and I havnt read the whole thing in a few years.