Hi Brady,
>When the SM 79 was being phased out and only the SM 82 and the Cant Z 1007 were in servie in Southern Italy
Actually, the S.M. 79 was employed against Malta alongside the Cant. The S.M. 82 was a transport trimotor, I guess you're thinking of the S.M. 84, which seems to have been a low-production development of the SM79. With the same three 1000 HP radial engines in each of these bombers, their tactical capabilities probably were very similar.
With regard to their ability to withstand fire: The S.M. 79 had a steel-tube fuselage frame that made explosive shells relatively ineffective. (The Hurricane was famous for its ruggedness for the same reason. It shouldn't be forgotten, though, that both aircraft still had full-metal wings.)
Wood on the other hand was very vulnerable to explosive shells, so my money would be on the S.M. 79 rather than on the Cant every time.
Regards,
Henning (HoHun)