If you're going to rivet a patch, do "wet patch" with a bead of sealant on the patch and the floor pan (I hear road signs make for great patch material). You can go an extra step and add a layer of fiberglass resin matt over the repair to really seal things up. Welding is always preferred and you can rent a welder for cheap. I was able to rent and MIG/TIG machine 3 days for $100 and wasn't charged for gas or wire.