Sorry about the delay in replying - My original post was deleted when my computer froze, and it put me in a bad mood for a few days <img src="images/graemlins/mad.gif" alt="" />.
in SA in the wilder sections don't you folks have many forms of nasty predators that would find a canvas tent full of sleeping humans attractive
Yes, many, many, many critters that enjoy the odd nibble of homo sapiens. These animals are found in the really wild sections (big game parks).
In which case the ability ot be 6 - 8 feet off the ground ontop of a steel box might be useful.
IMHO, not really. It might protect you from the smaller animals that are curious (leopard, badger, jackel), but wouldn't eat you. in fact, the scent of a human will probably make them pretty uneasy and they wouldn't come too close to a camp (especially if there is a fire) but if large predators (lion, hyena)want to eat you, 6 vertical feet is not going to stop them. Even elephants, rhinos and wildebeast wouldn't be put off buy a big metal trailer if you [censored] them off.
I think that roof-top tents are there mainly for comfort. If you do a lot of camping, then they are also convenient. If you are weary of what nature has to offer, they also serve to protect you from your own nightmares. but from wild animals? possibly only a detterent for the less hungry ones.