Before I spent the time & $$$ on a metal one ( Which I would have done if WD hadnt said something) Id take a shot at pvc. Ive seen some flat caps, same size as sch.40, but theyre DWV ( Drain,waste & vent).
Some clever DRemel work & time consuming bolstering up of the edge of the caps, each could be made Twist Off & On. Mite be able to buy a 3rd cal & harvest sections of the edge of one to epoxy onto the end cap edges where a slot would be cut to twist the cap onto a piece of thin walled ( thinner than sch 40, but same size). Id try to decide how fat a tube I could get in then call around to PVC sales places, irrigation supply houses, septic system supplies, etc & see if anyone has a busted piece of pipe layin around the size ya want. YOu mite even get away with ridin up with a hacksaw & buy your stuff & only take what ya want.
Better get enough O that pipe for Birthing Pains. YOu may build 3 to get one.
Be a lot easier to shape strap on a heavy walled pieced.
MIte need a heat gun to get the hacked off edges to fit, or, maybe put it on a grinder & buzz the 90* off where the flat of the cap comes to edge & just have a ring O plastic left, slice that & open it up & use the whole edge. If that works, youll need 4 caps to make 2 that you can remove.
MIte be ahead with a couple O these
quick release dowell fasteners
search that
like this
https://www.jergensinc.com/site/account/cStockpricecheck.aspx?item_cd=801416Tons O ways to make it & have it as storage & still stash some electrics.