I'd be cautious if you are considering driving off-road with the 'roo loaded up with firewood.
There was a recent thread on fjcruiserforums about rear door cracking at the spare tire mount after regularly carrying a substantial load of firewood in a 'roo. Hard to pinpoint the exact cause, but it's easy to add a lot of weight, and it's cantilevered out past the spare so there is a lot of leverage trying to tear the spare mount off the door. Additionally, the impact loading from jouncing along a rough road can be several times the static weight of the wood.
I'd use it for trash, and load the firewood on-board or on the roof.