Is it possible to use a dict in a scene property group?

Coding Python Support
1

I want to save a dict of random information to the scene, per .blend file, the dict updates fine but when the file is reloaded it returns to its defaults.

    bl_info = {
    "name": "Test",
    "author": "Test",
    "version": (1, 0),
    "blender": (2, 80, 0),
    "description": "",
    "category": "3D View"}

import bpy
from bpy.app.handlers import persistent

region_3d_settings = (
            "view_location",
            "view_distance",
            "view_rotation",
            "view_perspective"
        )

class Test_Variables(bpy.types.PropertyGroup):

    startup_settings = {"clip" : {"start" : 0.01, "end" : 100},
                          "viewport" : {},
                          }

@persistent
def pre_save(scene):

    self_vars = bpy.context.scene.test_vars

    for a in bpy.context.screen.areas:
        if a.type == 'VIEW_3D':

            for setting in region_3d_settings:
                self_vars.startup_settings["viewport"][setting] = getattr(a.spaces[0].region_3d, setting)

            for s in a.spaces:
                if s.type == 'VIEW_3D':
                    self_vars.startup_settings["clip"]["start"] = s.clip_start
                    self_vars.startup_settings["clip"]["end"] = s.clip_end
                    break


classes = (
    Test_Variables,
)

def register():
    for cls in classes:
        bpy.utils.register_class(cls)
    bpy.types.Scene.test_vars = bpy.props.PointerProperty(type = Test_Variables)

    bpy.app.handlers.save_pre.append(pre_save)


def unregister():
    for cls in classes:
        bpy.utils.unregister_class(cls)
    del bpy.types.Scene.test_vars

    if pre_save.__name__ in [hand.__name__ for hand in bpy.app.handlers.save_pre]:
        bpy.app.handlers.save_pre.remove(pre_save)

if __name__ == "__main__":
    register()