The Flux uses a motor plate that actually sticks out past the TVP's. So, it won't work on the XL or X TVP chassis. I think you could mount the battery boxes just by drilling some new screw holes in the XL TVP's.
I have a feeling that the aftermarket will soon step up to the plate with more chassis and box options. FLM already has a new set of Flux TVP's out.
http://www.fastlanemachine.com/PublicPortal/