Morning
Bottom line a welded boat is better,stronger and will remain leak free longer, all rivets loosen in time. having said that,on a practicle basis on a well made boat the rivets can stay intanct for decades of hard use. the weight of the boat dpends solely on the guage of the alluminum used in construction.
In terms of fishing my concern is more the noise a hull makes, while drifting, than it's construction.
Take care