I travel internationally regularly, and I use the UDG 21" trolley backpack. It's excellent and fits everything I need. I sold my S4 cos it was to big to travel. I don't get any issues with it at all. The only issue is taking out the gear for customs every time. I think it would fit most gear except the S4, NS6 and VCI400. Check it out.
So Far I have inside:
Kontrol S2 + Deacksaver
Kontrol X1 + X1 Bag
MBP 15"
Sennheiser HD 25's
Audio 2
Crane Stand
All cables.
Back up CD's,
2 USB's
Mini maglight
Mags (For travel)
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