With the elastic or rubber band folded twice over itself, it can block a parachute or streamer at ejection.
Here's that old solution to help keep the mount flat against the inside of the body tube.
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Glue the elastic at an angle as shown. Look close at the picture and you can see the cardstock mount has already been pre-creased.
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Here's the first fold. Note the loose end of the shock cord is laying beside the glued end.
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At the second final fold, you can see how the elastic lays beside itself in a "Z" shape.
Before gluing into a tube, I'll form it into a crescent shape to better conform to the inside of the body tube.
TIP: Many modelers use too much glue when making a tri-fold mount or shroud. More glue only makes a mess and takes too long to dry. Use more glue to glue a tri-fold mount inside the body tube.