I thought one reason for using spot welds was it deformed the sheet metal less.
Having watched Mick do it he used some rivets to get the fit correct, or the threaded thumb clamps, forget what they are called, if they will go in. With the thing located he would then weld in a way rather like tightening a cylinder head. This spread the loading along the seam. Once the spots were holding the job the rivets/clamps came off and the job was finished off, lastly filling in the original clamp/rivet holes.
Of course proper spot welders are a clamp as well. that is a problem when you cannot access one side of the weld, or the electrode energy is dispersed by being away from close proximity to the the other, on miss matched metal thickness. it can turn into a zipper, a known prob on Schmitt monocoques.
Interestingly the normal screen surround I have found on low production cars is a channel with rivets, not least as the channel is sometimes brass extrusion. It is more malleable and chrome's up nicely. Even tin bodywork is riveted onto brackets hidden under the surface. I actually have a box of Misc rivets for repairing such things. Though cheaper cars can have a panel with a hole cut in and the screen rubber mounted. This rarely looks well.
