8 months seems like a long time, but the longer you wait to get them in a helmet, the longer it takes for it to work.
Take the helmet off when he's swimming. Most helmets have a 23 hours on, 1 hour off routine so the hour off he can be in the pool and you can clean it.
As for cleaning, a rubbing alcohol/water mix will clean it; however, the only thing I could find that took away the smell was Wal-Mart brand, Parent's Choice Fresh Scent Wipes.
We went through Hanger Orthotics and they gave me a schedule that will help your child adjust. It may take longer because your child is older, but my son adjusted quite quickly at 7 months. If I remember correctly the schedule was:
Day One: 1 hour on 1 hour off (no overnight)
Day Two: 2 hours on 1 hour off (no overnight)
Day Three: 4 hours on 1 hour off (no overnight)
Day Four: 8 hours on 1 hour off (no overnight)
Day Five: 8 hours on 1 hour off (overnight)
Day Six: 23 hours on 1 hour off (overnight)
Since my son was already sleeping 12 hours a night, I didn't have him wear it overnight until he was at 23 hours a day. This is just a guideline, some kids need more time to work up to the 23 hours.
Talk to them about a schedule, my friend in Ohio was just given her son's helmet with no instructions and she struggled because she thought he had to start wearing it all the time from the beginning.
I know the helmet places near me in Virginia give free screenings and will provide you will all the information you need. I felt very confident using the helmet with my son after talking to the specialists.
If you have any other questions, feel free to PM me.
P.S.: If you do get the helmet, check out Blingyourband.com. They have so many decorations you can put on the band. The are not reusable, but they do come off quite easily if you want to change them out.