I use a Tripp Hard shell case for my sojourns. It's capable of being put in the overhead locker and isn't too heavy.
It's very strong (needs to be) and is lockable by both key and number code.
It's been kicked around the back of Sheds (SD360's), chucked into the holds of A320's, B737's and now dumped in the back of a Hawker.
I also shove a fairly heavy nav bag on top and the extender arms are still functioning.
I got it at Debenhams, I think it was about 55 quid. Money well spent.