There are gig bags and hard cases (lightweight ones, not a heavy wood case) that have backpack straps, available that would do the job nicely. If you use a gig bag obviously you need to be careful. Protec makes some decent lightweight hard cases with backpack straps that would work. I used to do this 40 years ago without any carnage to the horn, and know a few others that still commute on a bike, or motorbike this way. See if you can borrow a case or bag that fits your horn, and try it first to see if the weight/balance/bulk is something you can deal with.