Hey Stephen! Thanks for playing, I'm glad you enjoyed it. The ship has 2x Position2Ds on it to track where the line/trail starts at the back of the wings, and then 2x Line2Ds nested into a generic Node (this is important to stop their position from being relative to the ship). 
The entire script for the lines/trails is as follows:
Then all you have to do is hook that target_path for the LeftTrail to the LeftWing, RightTrail to RightWing, and fiddle with the trail parameters until you get a look that you like. To mirror the exact same effect I have, it's a width of 10, rounded joints, and the fill is a gradient that goes from fully transparent to fully opaque & red.