I use a flange tool (makes a countersunk lap seam on one piece) and Harris Stay-Brite solder and flux. It works quickly and the solder melts around 400~450 degrees so you don't have that warping and puckering. On things like doors, you can get everything like you want it, drill/rivet the panels, solder and then grind down the rivets and fill. That solder is as strong as you need and when you're done you shouldn't have much to grind/fill. There are several flange tools and some don't even cost $50. Harbor Freight has one for about $35 or so. Be sure to neutralize the flux with soda mixed in water or it will oxidize over time. If I have to do anything else, I'll use a brazing torch, but brazing must be done at a much higher temperature and a brazed joint won't be as strong as the Stay-Brite joint if you've done it correctly.
https://www.harrisproductsgroup.com/en/Products/Alloys/Soldering/Lead-Free-Solders/stay-brite.aspx
