I gathered the parts and assembled my 43 gph watermaker on Skipping Stone.
The first thing I did was find a good deal on the high pressure pump, as that is by far the most expensive item. I was able, after many months of searching, to find a nearly new one at less than half price, from a watermaker manufacturer who had experimented with it, but found it unsuitable for their project. Then it was pretty simple to assemble the other bits and place the pieces where space was available. I used Pex fittings for all low pressure lines (blue for fresh, white (I'd have preferred green) for salt water.
It worked trouble free for about 7 years, only needing a few inferior quality SS fittings replaced. I did incorporate a battery powered TDS meter into the system (under $25.00), so I could keep tabs on that without messing about testing the water. I ran a 12vdc feed pump and a 110vac high pressure pump.
There a lot of folks who get all fussy about the water quality from non-pristine seawater, spending money on UV systems, but from all my research, the membrane will not pass anything biological (or otherwise) that could be harmful to humans, and I used my normal tanks. That is not to say that it can be run in oily or fuel polluted water, and never in freshwater.
I figured it saved me around $3k over a premade unit. I still cannot enjoy a glass of water here, even after filtering, after living with RO water for so long.