welder/welding

On the trailer……..
I would weld it with a 6010 rod.
I would also add some gussets to stiffen it up.
I agree that stick would be a good option for structural stuff, but you were replying to RAT ROD AL's comment when he said to try 75/25. I believe he was replying to the OP's post and had nothing to do with the trailer repair. Slight miscommunication I think.