That lafette is already there at the very start, bots just man it, as any other static weapon.
About the bots behaviour, well, it's a well known fact they can be a little bit stupid about moving around, in different degrees, depending on the map. Actually, I felt the bots being more capable in Studienka after the last update, mainly on the German side. And that M10, at least during my last gameplay, moved normally throughout the map, crewed exclusivelly by bots. It crossed the bridge and actively supported my assault on the Fuel Dump.