I have a wilderness systems tsunami with the phase 3 seat and until recently have had no problems. Lately I have back pain after about 1 1/2 hours paddling. Anyone have any suggestions on a support or brace to use?
The first thing to try is stretching before you begin.
You might do better with a conventional back band rather than the back rest of the Phase 3 seat. Wilderness Systems makes (or at least made) a back band specifically for this conversion process, although other back bands could probably be adapted for use.
Here is a video describing removal of the Phase 3 back rest and installation of the WS back band:
That looks like a huge improvement over the original.
Though I have to say that I didn’t like seeing pop rivets being used. They rarely work like they’re supposed to.