I have used Lexol, but prefer the Montana Pitch Blend Dressing, and it goes a long ways, so buy a small bottle.
Clean leather with saddle soap, or Montana Soap Oil, then treat it with Montana Pitch Blend Dressing, with beeswax which adds water proofing.
http://www.mtpitchblend.com/ If the back quiver is made of medium weight latigo (horse hide), it will lay flat with a little use. Heavy weight leather takes some work to loosen it up. Cowhide should be medium to light weight, as it is stiffer, IMO.
The bottom is preformed, around a one inch thick piece of wood, cut to an oval shape, slightly smaller than the bottom with the sides stiched. Once it is hand sewn into place there is enough room for a dozen broadheads. Normally, I use a one thick piece of styrofoam, cut to fit inside. If you take the time to put the broadheads into the foam, your set. It will last for years. I have used small clippings from evergreen trees or bushes in the bottom.
If I was in the field, and noticed a rattle, I will remove the arrows and bend or flatten the leather and put the arrows back. If the chest strap is too loose, tighten it some to keep the quiver flat.