I think that the design concept of a 3 point mount is a proven thing. I was initially going to use one myself but chose not to after much reading and numerous discussions with people that know more about this stuff than me.
As mentioned, a dump truck uses a type of 3 point mount and they do just fine. Personally, for a Fuso frame, I think that if a 3 point mount is used then having the pivot at the front is preferable to having it at the rear, given that the most amount of flex happens at the front. As biggoolies has said, his camper is quite light too, which is a plus if using a 3 point mount. There is no pass-thru either, which also helps.
How to mount a subframe to a chassis has pretty much been done to death on this forum, so I will not try to try to hijack this thread and turn it into another on the same subject.
All I will say is that when it comes down to mounting a camper on a Fuso stepped chassis, I think the design has to take into consideration the weight of the camper and the type of terrain that the vehicle will be used on.
Do that and you should be fine.