Rusted Floor Pan welding suggestion

Hi guys, I'm just looking for some advice. I know that there are a lot of threads on this forum regarding floor repair, and they all contain very useful information, but I had a question concerning the welding aspect of this job.

From looking at the underside of my XJ, I will need some fairly major work, especially on the driver's side. Last time I checked, I had a hole almost the size of a football. So I will be getting some sheet metal and welding that in.

Now, I do not own a welder, but have a welder friend that owns a flux mig welder that he is willing to lend me. Would this do a good job? I've checked the tool renting places in my area and they only have arc welders, which I know is not the way to go on small gauge steel.

Another question is, should I be using 16 or 18 gauge? What is the original gauge on the floor pans, and would 18 be durable enough? I have read the other threads, and some mention they regret using 16 because it's not easy to shape it.

Thank you for any response or feedback you can provide.

Your going to need a "GOOD" welder with gas and .023" wire.

I just patched three places on my passenger side floorpan, none of which were flat. I used 16ga steel and didn't have any problems getting the new piece to match the flooring curvature. I think the trick is to cut your new piece BEFORE you cut anything out of the flooring, then set it over your hole and hammer it until it matches the existing topography. (I used a bodywork hammer I got at HarborFreight). Then, once you get it matched, trace a line around it in the floor so you can make your cut match the patch perfectly.
The MIG welder should do fine. Definitely use shielding gas, and I'd recommend practicing on a few scrap pieces beforehand if you are a little "rusty".

I feel your pain with rotted floor pans, a buddy is redoing his floor this winter and I plan on starting this spring, curse the salt!!!!!!!

Shielding gas makes things much cleaner, but using flux core is fine for floor boards and a lot simpler. You're going to grind all the welds down anyway, so who cares how clean and pretty they are. I welded all the floors and trunk in a '69 Firebird using flux and didn't think they looked bad at all after they were grinded down.

I panel bonded sheet metal in two spots inside and outside. It will last for ever and is completly sealed.