Question about siege guns.

[Serpent77]

Is a single siege gun unit enough for the whole stack (corpse or army, etc.) to receive a siege bonus? Or if one has multiple siege artillery units in a stack the time needed to siege a fort will decrease?
Another question - what will happen if enemy cavalry intercept my siege guns travelling without support units in the rear area? How good are they to defend themselves against enemy cavalry? (1 siege gun against 1 cavalry unit).

[Zebedee]

From my limited experience of the game, siege guns get captured by cavalry very, very easily. In my current campaign, I don't think I've built a single one but every one of my corps has at least a set