New Dilemma...

So, now that the bumper pad dilemma is solved I have a new issue. A friend gave me a bicycle trailer so I could take the baby out for a ride. I was so excited to use it, I got it all cleaned up last night, pumped up the tires and practiced riding with it before I put the baby in it :) Then I noticed when I read the safety instructions that kids had to wear a bike helmet in it and be over a year old. My son is 7 months and can sit up on his own so I didn't see the problem in using it. However, after doing a little reading online I found you aren't supposed to put a helmet on a child under a year old. Apparently, a helmet is heavy on their neck and bumping up and down in the trailer isn't good for their neck either. I am only planning on riding on pavement around my subdivision - not off-roading. My husband doesn't see the harm in putting him in it. Has anyone ever used one with an infant?