Why not replicate the missing cushion, using the adjacent cushion as a construction example?
On my 2000 380DA the sculpted cushion exterior was created by internal perpendicular fabric panels sewn to the cover fabric joints and stapled to the coated marine plywood base. That cushion construction required sequential assembly of the foam and cover to the base.
The difficulty will be attaining an exact fabric match due to age, fading and wear, but the result will be superior to the existing void.
Thank you wingless That's an option I've been considering. I've located a vendor that has the correct material and piping, but I figured I would reach out to our SeaRay community. Maybe there's a dealer or owner that has a cushion. Happy Boating!