It's been a long time, but I used some decent sized PVC pipe...maybe about 3 feet long. Glued some rounded end caps to each end...I had to then seal each seam with clear sealant (caulk) to make it airtight. A couple of barbed fittings screwed into opposite ends..everything available at a home store. I can't remember if I stuffed it full if something like polyester batting or not. There must be an ET2 users group somewhere. I assume there are a bunch of those arms out in the world.
Steve
Steve