For the 12VDC power, I would use a fuse, diode, TVS + bulk capacitance to give filtered DC with some hold time. I use massive 6,600W automotive TVS Vishay
SM8A27 which clamps to 40V with 75A impulse. It's a simple solution proven to be robust. Depends on how many $$$ the electronics is downstream.
The RPi SMPS thus does need need to tolerate the TVS clamping voltage, so good to 40V although the TVS does around 30V with smaller surges.
OP can you comment on the grounding on the boat, for lightning discharge ideas.
I don't know marine practices but I thought the engine gets grounded through the metal driveline and prop. But I see a ground plate is involved, and creates a new issue for galvanic corrosion between the two unless it's zinc. There is a ground busbar used as well on boats I see.