The weight of a sousaphone is mostly on the shoulder, but it does rest a bit on your hip. I don't play one, but a good friend does and i ended up putting one on some time ago. It wasn't horrible, but I wouldn't want to go though an 8 hour practice with one of those.
On the left my Bundy II that I've had for eight years, and on the right is my Yanagisawa A991 that I've had for 2 years. Just had my last HS concert this past Wednesday. I do need to find somewhere to play my sax at, I do enjoy it when I don't have the stress of HS band and just HS in general going after me. Now I've got college stress to worry about!