I added Gas struts in my saloon seating.
To find the right struts i used an Internet Tool like this
https://www.gasspringsshop.co.uk/gas-spring-calculator/For finding the correct weight of the moving part of the seating i used a spring scale (used for weighing suitcases).
I calculated the struts to hold the seat up in upper Position and leave the seat closed when in down position. So there is a little help when opening the seat and enough force to hold it open.
It showed that the struts will open the seat itself, when the boat is heeling, so it is neccesary to keep the locks closed when sailing. Maybe it's better to reduce the opening force in closed position. Hope this will help!