If I am reading the specs correctly the difference between the modular and the skin systems is that the skin are not padded.
Skin
This non-padded, lightweight, modular system allows you to organize your gear on all Think Tank belts, and work quietly with the Silencer Flap! Our 5 piece system is designed for a SLR user with 2 to 4 lenses and a flash.
Modular Set
Padded, easily accessible, Modular set allows you to organize your gear on all Think Tank belts.
So it appears to be possible to store, transport and deploy the modular cases on site. A duffel bag may not offer much protection if you want to store and transport this gear (plus I like to pack in my undies and toothbrush too....see my other thread)
What would be ideal is some sort of protective OUTER case (like a Pelican 1510-shell...or a stripped down TTP Airport Addict V2.0 shell only) and you just drop in your gear in the padded modular case and the belt and others stuff like a laptop and undies...and toothbrush. You reach your destination, take out ONLY want you need.
The only problem with my grand plan: cost.
The TTP system for storage, transport will include a holster.
Sterioid Speed Belt $47.50
Modular Set $169.00
Pixel Racing Harness $35.00
Digital Holster 40 $69.00
Total $320.50
Plus a Pelican 1510-$162 (assuming all this fits in there with room to spare for toothbrush/undies and laptop)