He's no more likely to get hit with the trailer than without it. In my experience he's probably less likely to be involved in a crash while towing the trailer. The only disadvantage of a trailer over a riding without it is the overall width and length. I have found that motorists give me noticeably more room when I'm towing a trailer. This is true regardless if the trailer is a child trailer, with or without child, a flatbed utility trailer, or a 14 1/2' canoe.