If you use Tenax or Proweld adhesives this works wonders and as a result I rarely use putty anymore. Stretch a piece of sprue over a candle. As you pull the sprue, you can see that it varies in thickness. The closer you get to the center the thinner the sprue. All you do is fit the sprue into the seam and dab the Tenax or Proweld on the sprue. The Tenax/Proweld melts the sprue forming a solid bond. After a few minutes, if there are any irregularities you can wet sand them smooth, (I use 400 grit). Since the plastic melts together, there is never any cracking or shrinking. I've been using this technique for many years and it is great! You can vary the thickness of the spure to fit any gap and since the sprue is so flexible, it forms around contours such as wing root leading edges, and even along wind screens where it connects to the the fuselage. Also just before the sprue is completely solid, you can smooth it with a blade and that keeps me from having to do much sanding. Good luck and drop me a line if you need any more help. Regards
Chris