Airix C-47; Milliput-not just for gir...erm... figure modellers :o)

Before the lower wings were fixed into place I glued a length of 4mm square styrene inside between the top and bottom joints to give extra strength and prevent any flexing of the wing roots.
Once everything had set firmly Milliput epoxy putty (I use the white stuff) was mixed together, rolled into a 'sausage' then worked into the wing joints;

Using an old paint brush the Milliput was worked into the joints and smoothed out;

Finally any excess putty that had gone into the panel lines was just scooped out with a needle and there you have it! The joints made good without losing any detail through sanding if regular model filler had been used;

Using this method of filling a joint is only possible if you have a firm area to work with, any flexing will just crack Milliput as it does'nt bond to the plastic unlike Humbrol or Revell plastic filler so it's a good idea to strengthen joints like this.
By the way I got this tip from Brett Green, editor of Hyperscale and Model Military Int'l so I take no credit for the idea, just passing it along to you lot out there :o)