You believe the rifle had previously been transported in Oswald's duffel bag. Oswald regularly had Marina do his washing when he went to the Paine's on weekends. He had not visited the previous weekend so there was no need for any curtain rod story. He simply could have used an excuse about laundry to Frazier and used the duffel bag to transport the rifle hidden amongst some clothing. There was no need for a paper bag to be constructed. But there was a concoction of a "curtain rod" story by Frazier.
Even disassembled, the rifle would have been longer than the typical military duffel bag and therefore would have had to stick out exposed to view (it was not possible to completely hide it among his clothes). The typical bag like I was issued had 3 grommets spaced at ninety degrees apart around the top opening that were placed over a fourth grommet which included an integral elongated ring. This procedure closed off the top and then a hook with a spring closure attached to the end of the carrying strap was then hooked to the elongated ring over the grommets to secure everything. If something thin (like a rifle) needed to stick out because it was too long, one of the three grommets could be left off of the elongated ring to create a small opening so the rifle could stick out. And the remainder of the top opening would be closed. Wrapped up in a blanket among the rest of their possessions, it apparently didn't attract suspicion from the Paines. But it certainly wouldn't have looked like part of his clothing if he took it to the TSBD.
In my opinion, the genesis of the curtain rod idea came from seeing the Paine's curtain rods (which were stored on a shelf in their garage). The were enclosed in none other than brown shipping paper similar to the stuff used by the TSBD shipping department. It is easy for me to believe that LHO most likely saw those curtain rods in the garage at some point. And just as easy to believe that his idea for getting his rifle into the TSBD disguised as curtain rods came from seeing them and the wrapping paper operation at the TSBD. It was a decent idea that fooled Frasier, and, if questioned by coworkers, he could have said the same thing to them.