I ran IB in my Subaru with IDQ subs and later AE SBP subs, and absolutely loved it, but a hatchback is a different animal. IB in a hatchback is not a great idea. In order to do IB correctly the rear wave should not interact with the front wave, this would mean that you would need to fabricate a rigid, almost airtight hatch cover, and you'd also want to build a baffle behind the rear seats because seat foam will do almost nothing to the long wavelengths of sub frequencies. If you can't do both of these things, a traditional enclosure will be optimal. IB has some great advantages, but in a hatchback it just isn't going to work without a lot of extra work, in that case you can build an oversized sealed box that would be far easier and sound as good.
