I use airflow fishing cushions yo sit on whilst fishing in my Sib.
I have one on top of my fishing box and one on my now box.
They are very comfortable to sit on.
Nothing worse than having a sore hind end from sitting on a rock hard tube or seat.
I got a local upholstery company to make me a similar cover for the bench seat as well.
60 quid all in for the 3 cushions.
Money well spent.