Just a thought here - but a backpack style carry solution will better isolate your instrument from road shocks and jolts. If you tie something to a rack, or lie it flat on a trailer there is less cusion between your horn and the railway tracks (or whatever). In a backpack you can add your legs to the suspensions equation for the instrument at will.

This is why my guitar goes in a backpack rather than using a rack or trailer.

Or course - the quality of your instrument case is also a big factor here.