We will likely go with a seat rail mount, but there's not a lot of room between captain's saddle and stoker's bars, thoughts?
Edit/adding info: This is the mount we're thinking about: https://www.topeak.com/global/en/pro...I-BACKUP-ELITE And I have a B-RAD in the tool box from another project that may be needed to adjust the height of the mount.
Will it work on the stokers seat post. Another option you may have already considered is a water pack. I use a 100oz Camelbak military version that has insulation oven on the tube. There is also 85oz Hi Viz that is insulated. There are also lighter weight versions with 50oz.