Now from my understanding a "Mig Welding Spot Weld Shroud" is a thing that plugs on the end of the welding gun and you just press and hold the trigger and it welds a spot weld ?
You can get the same effect by welding normally for a second or two without moving the torch. It's not like real spot welding.
It's not a reliable technique unless you have set up extremely well. Far better to use the plug welding technique instead (it is identical but you drill a hole through one sheet increasing the chance of a join).
And no, i don't think it does matter if you're using gas or not....gasless just spatters more that's all...but if i'm correct gasless isn't ideal for car panels...but i'm sure someone with more experience on that will soon show up....
I have a Clarke 90EN used gasless, which I use 0.8 gasless wire. Because of the nature of gasless welding I would try some test pieces on some similar scrap or off cuts before tackling the main job and to get a little practice to be satisfied with your result. Once you are satisfied and gain that confidence knowing that your work won't fall apart you will be able to tackle other jobs with gasless. I always warm up on some scrap before starting any task.
I have just purchased an Auto darkening helmet which permits me to see through the smoke gasless welds produce. I can weld 1.62mm down to about 1.2mm wall tube and plate without blowing holes now with perseverance and understanding about the method. Gasless isnt tidy and is unpredictable, but you can use it outside even if its a little breezy