It's more skills than equipment. Can you weld upside down on thin metal without making it a mess?

 

I have never attempted upside down, I do keep the mess to a minimum though.

 

There's no reason not to use flux core, though gas shielded MIG is better for thin sheet steel.

If you have doubts then you could go halfway. Get the rear subframe out, get everything cleaned up and prepared - then pay a professional welder to come over and do the actual welds.

 

<--- Professional welder

No way would I want to try this job with flux core. What happens is that the flux takes so much heat to burn off that the thin sheetmetal ends up melting away first, blowing holes everywhere that you now have to try and fill with weld using the same flux care filler that got you into this. If there's not a gas conversion kit for the HF machine then plan on going the epoxy route.

 

+1 for gas shielding.

Also, +1 for practicing upside- down. It's almost a different skill.

If you can pull a decent upside- down bead on sheet metal with flux, then, hell yah, go for it.
I have been welding for a long time, and know that I cannot.

t
the angle grinder is the best training tool for an aspiring welder...

 

flux core + structural + "I've done some welding" + upside down + Harbor Freight = too much risk for me.

I'd also recommend contact a mobile welding service and see how much of the prep they're willing to let you do.

 

I am an amateur welder. I have welded with gas aswell as flux. Like I said, I'm an amateur and far from a pro welder, but with the little experience I have I can tell: do NOT use flux welding for the rear subframe. Either you will burn through, or your welds will not be as strong as they should have been if you used a welder with gas.