Built a rowing frame for an old Shredder last fall– cut down a small double-rail cat frame and added a drop footbar up front. Also made a Jack's-type tramp seat (to keep the weight low) and got an inflatable backrest from Jack. She really likes the comfortable seat.
Here it is afloat this spring:
The oars are 7.5 ft. With one person, it rides high and she thinks it needs 8 ft. oars, given the height of the rainbow oarstands. I made 8 d-ring patches and glued 'em on to rig the frame.
Here's the rear view (note the fore/aft trim, which is ideal):
This could've been a single-rail frame, I guess, built like the light cat frame I just finished. Pumped up tight, the Shredder is stiff and only needs the frame to do three things: couple the oars to the tubes, provide a footbrace, and provide a place to sit with back support, and good weight distribution. (If you omit the seat and sit on the rear thwart, it buggers the trim.)
I might have used a seatboard and/or a plastic fishing seat like the one on my light cat frame, but the Shredder tubes are short and fat, and a board with a seat on top would put the rower way high and increase the chance of flipping. After all, it's designed for two kneeling paddlers which puts the design C of G quite bit lower.
Jodie ( a former raft guide and a kayaker) says it handles like she hoped it would, or better. That's my reward.
Have fun with yours—