HI, I use the 955 on a 42 boat, it's grp, but mostly lined with aluminium backed insulation.
I used to have the 240, but "upgraded" as I was getting such poor WiFi range. Unfortunatly the 955 is not much better and it struggles to get over 8 meters, I have reported this as a problem, but never received a response. I stick with the 955 as the 3/4G performance is very good, but to get over the WiFi range problem I have to use another brand of AP.
You may want to use MESH routers to get full coverage, espically if the boat is steel.