I don't want it to be in readable form and I can manage the creation of the format.
Simply encrypt it then. All files are somewhat readable/editable to some extent without it anyway. Using placement scripts can be very useful and has many advantages. The only thing that stumps me now is how to texture the terrain.
What about several dynamic quadpatch blocks which appear and disappear when in range with 1 large tile tex per block, scaled so the texture appears close to its true res on screen? A lot of the textures ie, for 'generic landscape' with no unique features could be re-used.