They were okay (!). Both 2.5 non-turbo diesels, so desperately under-powered anywhere but generally no problems. We drove extremely carefully off-road - more for fear of breaking components than anything else. We finished with 3 days on Fraser Island (the world's largest sand island) and they did extremely well in the Sahara similar conditions.
Lowering tyre pressure and careful driving are the key, they just get more important as you get heavier!
Would have liked a TDi though (as now fitted!).