Ethanol damage to fuel lines in boat

I know this topic has been discussed and the damage caused by the ethanol in gas is well documented. While gassing the boat I had a conversation with a guy who just spent 3K repairing his boat from ethanol damage. We all put that preservative in our tanks for the off season but his mechanic told him unless you are using your boat every week then you need to put that preservative in to protect your fuel lines from getting corroded by the ethanol.

Was curious what everyone's thoughts are on this area. I am typically 3 weeks maybe between outings. Is that enough time for the ethanol in the gas to cause damage? I am thinking that as the years pass it might be so would it be better to put some stabilizer in after every trip out on the water for preventative reasons?