I would be concerned about the strength of the roof also.
I have a 99GV, and at some point in it's life a previous owner obviously put something one the roof, as there are dents which are not really noticeable, but if you look for them you'll see them. The roof itself is not that strong, but it is apparently reinforced at the appropriate locations for the rails.
Suzuki says not to put stuff directly on the roof, the OEM roof rails and crossbars are rated at 45kg or roughly 100lb, I have no idea what your tent with you inside it will weigh, or what percentage of that weight will be on the roof, but I'm guessing it'll be over 50%.