gas flux core
yes you can use gas with gasless flux core , in the old days industrial welders us to do thsi until flux core became better, but in general it is kind of over kill, but on the other hand in the industrial market there are flux core wires that requires gas (co2 flux core) used often in heavy metal fabrication.
but i general and use hot rodders alway think we can invent something new,
its boring but follow manufactures reccomdations but it will work in this case
being a good welder require practice and experience, and being agble to handle to ever changing conditions for each weld.
but for most auto hoby work i would reccommned bare mig wire with gas, and then maybe regular stick welding for frame and suspensions