Well since I have a Mach 1 its obvious I don't have the Mach 1000 but. I've seen several and I'd have to say there really isn't any place to put it unless you want it right in the center or something. You can't mount it up right behind the seats cause the amp rack is there and the sub on either side takes up the little nook most people put it in.
There is enough room behind the seat for the battery, I keep my gear bag back there and that is alot larger then a battery, Look in this months issue of MM FF they have a mount that actualy mounts batteries below the rack, looks GOOOOD.
Well www.chicanesport.com sells a relocate kit that you're looking for... but unfortunately their site is temporarily down. Keep checking, hopefully it's just temporary.
This is an exerpt that I saved while the site was working:
"Many customers are installing components that require the relocation of the battery to the rear of the vehicle. Usually, this means purchasing a battery relocation kit that includes a battery box which takes up precious trunk space.
For those customers fortunate to have a vehicle equipped with Ford's excellent Mach 1000 stereo system, we engineered a relocation system that takes up almost no additional trunk space, is really trick looking, and is a functional alternative to the traditional 'box in the trunk.'
Our trick system is constructed from billet aluminum and houses two Optima thin-profile 6-volt batteries that are wired in series to create a 12-volt system.
The unit installs using pre-existing holes in the mach 1000's amp bridge/tray."
The two batteries sit underneath the amp rack of the mach 1000.