MAGNESIUM ANODES...NOT the zinc they come with...
the one behind the prop is IMPORTANT
you got bad info from manufacturer about "the ones they come with" Zinc only in pure salt or heavy brackish!
and you can add more mag anode for more protection. I added these this year, in addition to running magnesium in all other locations from the start. See pic. The addition of these on both sides of my caps STOPPED the damage to the caps. These were heavily eaten in 8 weeks in the water...doing their job! They are side mount outboard anodes by Canada Metal. $7 apiece.
I have massive amount of stainless (wing plates ect) creating even more of a problem, leave my boat slipped for 3-4 months in a boathouse with shorepower on and/or all around me, and after 2 seasons have very little damage. The bottom (raw) edge of the top cap, and the diameter of the lower behing the prop are the only spots and it's minor. It's the proximity of the S/S (prop, wing plates) to the aluminum case and the immediate proximity "battery effect" (electrolosis).
All the mess is from the muffler project I was doing at the same time.