Should not be an issue .
I have done trips up to 2 weeks duration in Australia's tropics on saltwater with no freshwater wash available with no issues on Revo 13 's with yakattack aluminium track systems which would be similar to the rails on a PA12 corrosion wise .
You could try giving areas of concern a wipe over with a suitable salt removing spray such as CRC tackle Guard or even give metal parts a pre trip wipe with WD40 or similar .If you are really concerned a light coating of lanolin spray on metal parts prior to leaving wont do any harm .
I am heading off in a fortnight to an island off the WA coast for 8 days with my 2015 PA12 and it wont be getting a wash till we get back .
have a great trip !
2015 Hobie Pro Angler 12 , Hobie Revolution 13