I have a lund alaskan that has rivets and it’s dry as a bone.
I think it has to do with how you treat / handle (don’t abuse it) the boat... mine is also only 4 years old..
I have a small Starcraft runabout that's riveted. I don't beat it up, and I don't think anyone else did either. 75hp Johnson, so it is fully powered...dry as a bone too. 59 years old. My son had a welded Tracker that kept cracking.
