Quick question about colliders

Ive been looking around for how to properly do collider with moving or complex objects, But it seems to be mixed.

I have a tank model, imported from 3ds with the Generate Colliders checked. This works fine when static and First person controller comes into contact with it, But when applying rigid body and gravity it falls though the ground, Also fast moving objects just go straight through.

I have applied a box collider to it and that works, but its to simple and leaves it collidable in huge open space where it wouldn’t be like under the barrel.

So, How do you properly add collision to complex models, You could just made a tonne of box objects and map it out into a prefab, But that seems like to much work epically when it comes down to collision detection, For where the object hit.

Prefab detection is quite bad when it comes to high speeds to fix this cast a raycast infront of the object so it detects a collider.

making a few box colliders is really the best way(less tasking) unless your mesh is simple.