Two things that go well together, Spectras and FPs.
Therapy is right, membranes have a shelf life of about a year or so if they remain sealed in their original packaging. This is why I don't recommend taking one for a spare. In your case there are a few things to understand that are important. First, the life span of a well taken care of membrane inside a watermaker
is on average 5-8 years. Even though there are rare cases where they last longer yours is more likely near it's natural end. Since the distance is great and it can be more costly to ship a membrane down to PR or elsewhere outside the states, I'd suggest to just take one with you with the intention of just changing it out when you get there. Secondly, though chrsjs means well, never, ever, get any other storage
solution besides Spectras SC-1 near your Catalina
. Sodium meatabisulphite will pickle the membrane but, as you probably already know and for the information of others with a Spectra, SM will destroy the Clark pump. If you are the original owner of this watermaker
the Clark pump is warrantied for as long as you own it. SB will void that warranty period. Thirdly, Spectras are a whole different catagory of watermaker. 360-400 ppm is not unusual especially considering the age of the membrane. But PR is in a warmer and higher salinity zone than other parts
of the world so I wouldn't be worried about that reading at all and if pressures and flows are proper would say that's a good ppm range. Fourthly, given your intended route
to the South Pacific
I would certainly not only recommend a membrane change but, if you do not already have one, a spare feed pump head
on board as well. Also your 2005 Catalina did not come with a boost pump. All new Catalinas do and for good reason. Spectra has found that a boost pump is making their feed pumps last a lot longer, I'd highly suggest you consider this addition. It's a simple retro fit. If you ever need any help with your Catalina don't hesitate to send me a PM.