Ok, the battery compartment is made out of 1.9mm thick steel, which is thicker than both the chassis and the ute floor, and can stand to cop a nasty dent or two without cramping the battery enough to damage it. In addition to this, in order to dent the floor of that compartment, it would have to be a hard drop off something directly onto a rock or stump, and then, it's strong enough to hold the back of the ute up in the air (even fully loaded). And, if you WERE to drop the car onto something like that, you'd rip the whole rear valance and subframing out of the ute as you roll forward (if you didn't have a good towbar or this compartment). There's plenty of FAR more delicate items under the back of the car to look after, apart from the fact this addition actually GIVES protection to the car's underside.
One point I can see that some people are missing is... THIS IS NOT WHERE THE CAR'S STARTER BATTERY WILL BE. This is just for the extra battery that runs the fridge and camp lights. You could set a grenade off in there and it's not going to have much effect on whether you can still start the car and drive it home or not.
Moreover, The safe little areas left either side of the "huge spare wheel carrier" up against the cab wall, are reserved for the FRAGILE, EXPENSIVE and quite VITAL fuel pump and surge tank units. It's not like the auxiliary battery could fit up in one of those spots anyway, and even if it did, it would be hanging below the level of the floor right where you're most likely to scrape a big rock or exposed tree root (if you've ever looked under a car, you'd know how many scapes and dings they end up with in the floor and chassis sections)...
Rant over... For now...

Steve.
- BARNES AUTOMOTIVE TECHNOLOGIES -