I've been playing, recycling my old mash tun for a summer 9L corny solution. I already have a mini CO2 bulb reg, but 16g cylinders get a bit tedious - I've been looking at the paintball and sodastream CO2 options for a while. I've gone for sodastream, as 425g is a good amount of gas and they are £9 exchange in the supermarket.
Once you have a bigger bottle it seems sensible to use a coolbox, as you can fix the bottle vertically and also mount a tap - and, um, keep it cool too without buckets of water etc.. I had to attack the lid with a Dremel as you need quite a bit of height clearance, especially with the discos, and even this massive (too big) coolbox isn't quite tall enough. A smaller and taller coolbox would be good, but I don't think they exist...
The existing super-portable rig:
Hacking a coolbox (I will fill the lid with expanding foam when I've finished):
Sodastream bottle and reg:
Cheers:
Don't need it at home!
) The reg came configured for sodastream (no adapters) - I got it from Hop & Grape, it was quite expensive, but an extra £20 on top of a cheapo reg+adapter seemed worth it for such a well designed compact unit.
Unlike yourself I don't have a keggorator so this is my only way to dispense,I usually only brew to 19 litres and I bottle the other half using a Blichman beer gun.
Something that you can just squeeze two 9L cornys in would be perfect. Anything bigger and I just as well take the chest freezer.... 
