Aluminum Welding

So I’ve made a few things with my MIG. Not a pro by any means.

I have a all aluminum cargo trailer I’m converting to a toy hauler. I want to weld in some support tubing around the window cut outs.

Is there anything special I need? Roll of wire? Has mix % Helium/Argon?

It doesn’t have to look great. I just want to tack in some 3/4"X1" tubing to support the window better.

Tips and advice welcome.