I own some fly rods. OK, too many fly rods. I needed a way to store them that didn't involve them stacked like cord wood. As is, this will fit most hard cases. For cloth covered hard cases you need to upsize about 5%. There is a divot in the bottom bracket for Tenkara. Or you can downsize to fit more snugly. 

Version 1 uses a retention bar to trap the case. You need two of the covers. Glue one side of the U shaped cover over the outside of the retention bracket, insert the bar and glue the other side. When mounting make sure to leave about 6mm between the top of the case and the bracket. 

If you don't want to mess with gluing and the moving bar you have V2 with no moving parts. You need the bottom of V1, and the V2 bottom. V2 bottom will allow you to insert the case into the top and drop it into the bottom bracket.

There are two spacers to help with mounting. Mount your bottom bracket, lay the spacer on it. Place your rod case on the spacer and place the top bracket on top and mark the holes. then remove the case and spacer.