Haven't had much time lately to spend modelling. Still in the process of filling and sanding. As said before its Airfix. The wing root joins are not panel lines as far as I can tell but they are as deep as and 4000 layers of Mr Surfacer hasn't helped. Should've used epoxy instead and might still have to. Will post an update soon. I hope......
Stretched sprue works pretty good depending on the gap. For really big gaps I use epoxy. Just be sure to trim it before it fully dries or there will be more sanding. Usually I use JB weld epoxy. Easy to use, easy to clean up.