How to implement a BaseViewController through storyboard or xib?

Question

Wait, I know this question title looks very duplicated, but it really is not.
I have been searching for whole day but cannot find any good solution.

Definition of terms

BaseViewController: A class that extends UIViewController, responsible for some common behaviors across different subclassed ViewControllers.
VC: Short form of ViewController, I will use it from now on
dialog: In other words, popup; a VC that does not cover the whole screen, and is present modally.

Scenario

Let me use an example to illustrate my needs.

Let say I have an app that displays dialogs in different places.
These dialogs have something in common, including:

1. They will blur the background when displayed
2. They have a same width
3. They have a same dialog container style (e.g. rounded corner radius)

And they also have non common things - the content inside the dialog container.

In order to reduce code duplication, I want to create a BaseDialogVC to implement the above 3 common things first, and then child class that subclass BaseDialogVC will provide the view inside the container.

Therefore, I created a storyboard file which contains BaseDialogVC and implemented the 3 common things using Interface Builder of storyboard.
It has an empty UIView that acts as a container for its child class to provide their content.
And then, I created a subclass of BaseDialogVC, for example, AddItemDialogVC. This AddItemDialogVC is then responsible for providing its content view, and the logic of this dialog.

Then I am stuck - I tried to instantiate from storyboard an AddItemDialogVC, but it will crash because storyboard does not have AddItemDialogVC. It only has BaseDialogVC.

Question

Actually, I know one alternative that can achieve similar things.
That is - I do not subclass BaseDialogVC, instead I instantiate it, and add subview to it by calling an instance method of it, passing in an UIView.

But I still very much want to know what's wrong with my original approach, or,
What is the best approach to this problem?

By "the best approach", I mean it effectively reduced duplication and is easy to maintain.

What I have tried

I found this post for changing BaseDialogVC to AddItemDialogVC. But even if it successfully created an AddItemDialogVC, the AppItemDialogVC cannot init its content view (A custom View that is subclass of UIView, and I got an "Thread 1: EXC_BAD_ACCESS" exception.

I think the most similar question out there is this thread.
However, the accepted answer does not elaborate enough; while the second most voted answer is the same as set_object that I have tried before.

FYI, my class for AddItemDialogView (NOT VC!):

class AddChoiceDialogView: UIView {

    @IBOutlet weak var rootView: AddChoiceDialogView!

    override init (frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }

    required init? (coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        commonInit()
    }

    private func commonInit () {
        Bundle.main.loadNibNamed("AddChoiceDialogView", owner: self, options: nil)
        addSubview(rootView)
        rootView.frame = self.bounds
        rootView.autoresizingMask = [.flexibleHeight, .flexibleWidth]
    }

}