OK
first install a RACOR fuel water separator
I choose RACOR because they have a clear bottom you can look at ( I/O boats need the metal bottom not the clear bottom, due to USCG regs)
Then run STABILIZER and keep checking water sep, before each run or after each run of the day
this will save you big $$$$ later down the road
If you have water use this to check and make sure
http://www.channelsupplies.com/paste.htm
IF water is present use
http://www.sentrytreatments.com/shtml/whysentry.shtml
also these 2 are great for an additive
http://lubecontrol.com/fuel.htm
http://www.fuelmedics.com/