About 20 years ago a lady asked me if I could make a rucsack type harness for her hard shell guitar case. I designed one with a strap which fixes round the waist of the case and a strap around the neck of the case, there was also a strap to go under the case. On the front side there were two shoulder straps. She still wears it at festivals. For traveling I made a single shoulder strap with a similar strapping arrangement for my banjo case. I find it very handy when carring a suit case and flight bag.
Cheers Bill