3M Panel Bonding Adhesive. You will need an Applicator, either 8117 or the economical 8571. The replacement nozzles are 8193. It gives you 90 minute work time to ge the panels in place and you need to leave it clamped for at least 4 hours depending on the temp. I would not use to overlap panels where you ar egoin to do body work over as it can expand and contract slightly and show a bond line where a cosmetic seam would be. It's great for roof panel, bedside and quarter on newer cars. Grind both surfaces with 80 DA to bare metal, the apply and spread over all bare metal to prevent corrosion and then add a filler bead on one panel before clamping both panels. Videos on YouTube under 3M Tech Tips Panel Bonding Adhesive.
It makes a great repair adhesive for steering wheels. I prefer to mix chopped fiberglass fibers in with the adhesive when going over cracks or building heavy areas that need extra strength.
It can be used as a rigid seam sealer as well. A great product for the drip rail channels.
Its an excellent rigid seam sealer over floor panel welded seams. it can be sanded and smoothed for finishing invisible seams on floor panel seams.