@jay.graw Is correct, both the under-slung weapons and the tick pod on a tank can be taken out. Against a military tank, the tick pod takes maybe 20-25 rounds of 7.62 from a 5-crown AI-76, the guns take roughly 75 rounds. Neither really shows any outwardly visible indication it’s taken damage though, and explosives don’t do a very good job of damaging either (even direct hits from the Gvg don’t do much).
As far as the harvesters, same applies to both their tick pods, and the missile pods they have (the missile pods stick out over the top of the back when you’re looking at them, they look like black or dark-gray pods with a bunch of holes a the top). Similar damage required here, though the two missile pods have linked health, so just pounding on one will take out both.
For the tanks, dropping both weapons actually deals a pretty significant amount of damage (also, the optical cluster just above the weapons is another good way to reliably deal a lot of damage), but for the harvesters, not so much.
Note, however, that there is no way to stop them from using gas or the concussive shockwave attacks they will use if you get too close, so make a point to still keep your distance.