Have a 38gal tank on the Ranger 188vs. I put the Stabil 360 marine formula additive in it & keep it full to combat the water build up from the ethanol in the gas. Question is for long term storage say a year or so, is it better to rack off all the gas & start fresh later or let *** ride? Most additives say it keeps gas fresh for up to a year.

Ethanol works the other way. The more fuel in the tank the more water it will absorb, so an empty tank is the best option.  Most additives do say they will work that long. My problem is the additive company will not repair my motor if it does not work. I purchased a case with a special 12 volt pump and hoses to pump the old fuel out.  You might consider doing the same.