All the negatives of fuel related condensation and other E10 issues are due to be ended once and for all, none too soon, with the implementation of laws to close the fuel system in boats, just like our cars have had for 30 yrs.
Why it took so long is because we boaters have not complained loud or long enough.
The law has been passed.
Off course, having a leaky fuel fill or ventf itting will do the damage irrespective. Same goes for the sender seal as mentioned.
Phase separation cannot occur with conventional fuel, and conventional fuel does not attract moisture to the same extent as E10 does, also E10 has a scrubbing effect to clean the scum including varnish off inner tank walls and hoses which will pass through filters.
Water separating fuel filters like racors and others would block the water when picked up off the tank bottom, no such activity is likely with E10 once separation occurs.
Water is not as bad as 100% ahcohol dissolved water mix, which I understand is corrosive. Nothing wrong with burning water as long as dissolved in the gasoline part of fuel.
The advise about filling the tanks for off season storage was always that, with use of a fuel preservative, in part because an empty tank is one big bomb and less safe to be around should an ignition source find the wrong place, and also due to less inner surface area exposed to effcets of condensation from fdaily expansion and contractin such in air, and water subsequent build-up at bottom of tank.
Same advise from Yamaha is offered for my 2 stroke oil tank in boat and oil tank on motor, keep it full for off season to mitigate condensation effects.
To use the manual switch on the motor to over ride the hi cutoff and fill it all the way.