Hello NS_Koty, this is the way I set up a typical vehicle with a turret using a hier:
[_ROOT_]
VisibilitySphere 3.08835
CollisionObject sphere 3.06028 0.0 0.0 0.0
[Body]
Mesh Body
Parent _ROOT_
Attaching 1 0 0 0 1 0 0 0 1 0.0 0.0 0.0
CollisionObject Body
[Head]
Mesh Head
Parent Body
Attaching 1 0 0 0 1 0 0 0 1 0.52 0.10 1.50
CollisionObject Head
[Gun]
Mesh Gun
Parent Head
Attaching 1 0 0 0 1 0 0 0 1 1.50 -0.08 0.42
CollisionObject Body
The head and the gun I usually centre in the 3D programme before I extract them and then use the hier to put them in position, that way the turret will rotate around its centre pivot and likewise the gun wil move up and down around a set point.
Shadows I add to Body, Head and gun. The turret rotation means there really should be a shadow on the gun barrel but the shadow on aturret is not always obvious when viewed in game as the main shadow seems to predominate.
I think each part should have a hitbox but you can I think get away with just one attached to the main body but covering the area taken by each part.
I never actually added Lods in the vehicles I got mobile but they should be added I guess for completness.
Have a look through this pack I put together:
https://www.sas1946.com/main/index.php/topic,51617.0.htmlHope this helps.
Wishing you all the very best, Pete.