Where to tie neutral to ground?

I'm installing two parallel outback 12v 2000watt inverters using the Mate and Hub in an off the grid system that will eventually have a backup generator. I will have a breaker enclosure between the inverters and main power center that will house the bypass/ inverter output/ generator input breakers. Right now I'll only be utilizing inverter output breakers in the bypass enclosure until I install the generator and the bypass/input breakers at a later date.

My question was where to tie the ground to neutral. I discovered that it should be at the main power center. Now my question is a bit different: When I install the generator, how should I treat the ground and neutral? Should they be seperated or kept tied together, how does the second neutral input from the generator affect if/where I should tie neutral and ground together?

Outback bypass breaker wiring diagram:
http://www.outbackpower.com/pdfs/wiring_diagrams/4-7-2kw-120vac.pdf

Thanks,

Wooo