I tried the GEAR seat covers and got rid of them. There's not much rear-seat room to start, and the kids didn't like to have stuff in their face. Also a potential for injury during an accident.

I do have the GEAR rear hatch cover in my 4-door Wrangler (JKU), but I don't think that idea would work with your lift-up hatch. But this is where I keep about 30 pounds of tools and my main first aid kit.

I don't know about the Liberty, but in the 4-door JK there is a huge amount of room under both front seats and the rear seat. Plenty of room for medium-size organizers filled with food rations, water, gloves, flashlights, etc under the front, and I've managed to fit entire drive shafts under the rear seat, along with my boots, umbrella, jumper cables and recovery bag.

In the back there is probably a compartment under the floor where your spare tire, jack and such are stored. There's usually some room there.

From a safety perspective, be careful to strap-down anything heavy with ratchet straps to prevent them from becoming projectiles in case of an accident.

For long trips I either load my stuff onto a utility trailer (easiest to deal with when camping/wheeling) or put on the roof rack and cargo box (family holidays).

Good luck with the new wheels. Let me know when you want to talk about a lift, big tires and a winch. ;^P