Struggle with SplitView

cbro_ot

Following is a split view with forms on the left "panel" and a rectangle serving as main area on the right.

import QtQuick
import QtQuick.Controls
import QtQuick.Layouts

ApplicationWindow {
    visible: true
    minimumWidth: 640
    minimumHeight: 480

    SplitView {
        anchors.fill: parent
        anchors.margins: 10

        ScrollView {
            ColumnLayout {
                GroupBox {
                    title: "Form 1"
                    Layout.fillWidth: true

                    GridLayout {
                        columns: 2
                        Text { text: "Lorem:" }
                        TextField {  }
                        Text { text: "Foo:" }
                        ComboBox { }
                    }
                }

                /* Spacer */
                Item {
                    Layout.fillWidth: true
                    Layout.fillHeight: true
                }

                GroupBox {
                    title: "Form 2"
                    Layout.fillWidth: true

                    GridLayout {
                        columns: 2
                        Text { text: "Bar:" }
                        RowLayout { TextField { } Button { text: "Yes" } }
                        Text { text: "Ipsum:" }
                        TextField { }
                    }
                }
            }
        }

        Rectangle {
            color: "navajowhite"
            Layout.fillWidth: true
            Layout.fillHeight: true
        }
    }
}

This has currently many issues which I'm not sure how to approach:

Dragging the vertical split to the left causes a scroll to appear (which is expected), but dragging it to the right doesn't cause the group boxes to expand (the fillWidth: true seems to only work for the initial state).
The spacer between the forms has no effect: I was expecting it to push the 2nd form down to the bottom of the window (it works if I remove the ScrollView)
I can't find a way for the margins: 10 to work within each side of the split view (having that property in the ScrollView and the Rectangle has no effect)