So, how did you get your name? Just asking...

gave it to myself!!

Hi S-man

Is anyone going to have go?
Millions of revers osmosis kits and individual filters on the market.
Get a filter - push water through and that's it.

Bad new- they all perfect for dirty and brackish water but density of
any of those is not sufficient for salt water.

For salt water -
"nanofiltration is used for the removal of contaminants from a water source, it is also commonly used for desalination "

You need nanofiltration membranes enclosure. /name of the filter/
How you get extremely high salt water pressure, I don't known.

just forget about home made unit and go for
Katadyn Survivor 06 Desalinator for Sports & Outdoors

I see one for $500 S/h tow behind boat 1gh per hour!

Looked at building my own and found that to be really hard and not cost effective - parts from all over the world and the pump is very expensive. Best (IMO) is to go to someone who has already done it and is making many - get benefits of multiple unit pricing from suppliers.

After considerable searching, found this manufacturer:-
www.cruiserowaterandpower.com/

VERY helpful people and I bought a 30 GPH unit - which works like a charm, produces lots of sweet soft water and is built with quality components.
It's manual operation and simple, with no proprietary parts.