Yes it is member variabled my TestHUD.h looks like this
UCLASS()
class ATestHUD : public AHUD
{
GENERATED_UCLASS_BODY()
TSharedPtr<class STestUIWidget > TestUIWidget;
void BeginPlay();
void DrawHUD();
};
Like I said the knowledge I had of Slates was basically just from the tutorial I followed however I have done more research on them now and well there seems to be a lot more to SWeakWidget than I originally thought.
In terms of just adding the TestUIWidget to the viewport I did try this
GEngine->GameViewport->AddViewportWidgetContent(TestUIWidget.ToSharedRef());
However the result was still the same