The manual is right, you want the trim stick in place with the curtain stapled to it, and the bolts tightened before finishing the stapling of the curtain at the rear bow. You also want the frame locked down in front for this step. The rear curtain doesn't need to be as tight as a drum, but it should be good and snug. Just don't lose your bow height while you're doing the curtain. It's more important for the curtain to be snug side to side than it is from trim stick to rear bow.
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