I've been investigating this exact same issue for similar reasons (we don't have the body roll problem).
It looks like - and while the jury is still out, this is the way I'm currently leaning - the Firestone Air Bellows are the way to go.
Rather than a single point of contact at the top of the bellows, there's a metal plate that spreads the load across about 150mm of chassis (give or take a bit). The bottom is bolted to the axle via a cradle that is u-bolted around the axle. This is an improvement over the single-contact-point.
IF you don't OVERLOAD the rear of the vehicle then you'd have to think that you'd have no problems with this at all. By "rear of the vehicle" I'm referring specifically to any weight that is behind the rear axle - anything forward of that would share the load between the air bellows, the leaf spring and the front springs (reasonably proportional to distance from those points).
As I said, I'm leaning towards them. RLI told me that he had a pair on his Navara and had no trouble with them. Others have voiced their similar opinions on this forum. Other forums have again been similar - the Firestone bellows are, it would appear, a good choice.
I'd like to hear from someone that has had a chassis failure and know the following:
1) What brand of bag was fitted, and if Firestone, was the top bracket fitted or was it excluded to conserve space?
2) How much load was behind the rear axle at the time of failure?
3) What was the vehicle doing both at the time of failure, and in the hours leading up to the time of failure?
With respect to 3), I'm not interested in hearing "We were travelling along the Stuart Highway south of Marla" while excluding the actual pertinent information of "we were doing 130km/h along the Oodnadatta Track all the way from the Pink Roadhouse to Marla with 500Kg slung on the towball".