I have been traveling with a spring metal framed Easy Soft box EB-60 60x60 and/or Easy Soft box EB-60 40x40 which are great little softboxes for using with Speed Lights but are not that light and are a bit of a pain in the luggage because of their shape and size when packed down.
I found a cheaper umbrella type softbox made by Phottix which is slightly larger at 70 x 70 cm, lighter and packs down to a smaller, long thin package.
Only problem (and there always seems to be a trade off when you go
cheap) was that the flash mount placed the head of the Speed Light very
close to the top of the inside of the box. Actually touching the box
when mounted on a Pocket Wizard FlexTT5.
So I designed and built this flash mount yesterday.
I designed the holder in ViaCad 2D3D and printed it in my Makerbot Thingomatic 3d Printer,
As you can see in the photos it brings the head much closer to the axis of the umbrella. The Nikon SB900 head simply presses into the holder and stays put using friction.
If you want to print your own I have put the stl file on Thingiverse.