I borrowed KF's Prism a few years ago. I had always taken a scrap 7ply plywood board for cleaning fish. It was kind of traditional and it developed a nice tooth over the years. Anyway one day near the end of that trip I stuck in vertically behind the seat. It was a fantastic backrest wedged between the seat and a thwart. 8" wide 2 feet long, no paddling issues. It was great. Comfy. In my tandem I'd lay back once in a while and crack some issues but I really enjoyed the serendipitous aspect of something so simple and arguably useless providing so much pleasure. I didn't trust laying back in the solo as it was new to me at the time. Second last day of the trip my line got caught on the bow's skid plate ;) Once I realized my arms were not long enough to get it out, I had to crawl back to the seat thinking damn, that was really a stupid move in a virtually empty canoe.