Django FileField with custom storage still uploads to default storage (GoogleCloudStorage)

Question

I want to upload files to custom storage, other than the one for static. But each time when i try to declare a custom google cloud storage bucket, it still refers to the bucket related to statics (probably to the default storage)

I am trying to Declare a new class from wagtail's AbstractDocument class

    class VirtualVisitDocs(AbstractDocument):
        file = models.FileField(storage=CustomGoogleCloudStorage(), verbose_name=_('file'))

Then using it as a foreign key for another wagtail page with document chooserpanel as follows:

virtual_visit = models.ForeignKey(
    VirtualVisitDocs,
    on_delete=models.SET_NULL,
    verbose_name=_('Virtual Visit Zip File'),
    related_name='promotion_pages',
    null=True,
    blank=True,
)


        MultiFieldPanel(
            [
                DocumentChooserPanel("virtual_visit"),
            ],
            heading=_("Virtual Visit"),
            classname="collapsible collapsed",
        ),

The storage instance from above CustomGoogleCloudStorage is the one which I have declared as follows:

@deconstructible
class CustomGoogleCloudStorage(GoogleCloudStorage):
    def get_default_settings(self):
        default_settings = super().get_default_settings()
        default_settings['bucket_name'] = settings.GS_VIRTUAL_TOUR_BUCKET_NAME
        default_settings['project_id'] = settings.GS_VIRTUAL_PROJECT_ID
        return default_settings

Each time I try to upload documents this way, I get HTTP 403 which is correct, cause the service account I am using is not allowed to make changes on the default bucket. Rather, I want files to be uploaded to the second bucket where my service account is allowed to create bucket instance objects, but I just can't point to that another bucket. Whenever I try to print custom CustomGoogleCloudStorage instance as a dict I get correct project ID, bucket name and credentials file