Lunds are great boats. I've seen plenty of Lunds take plenty of abuse in the walleye tourneys on the columbia and hear no complaints. We fish out of a welded crestliner and a welded Triton (Crestliner hull) and my next boat is either going to be a Lund Pro-Guide or Crestliner Pro-Tiller, whichever I find the best deal on. I haven't paid much attention to the welded linds but I've never heard much bad about their rivets either. Several friends of mine have lunds that are over 20 years old and never had rivet problems.
Good luck wih your search!