Need help with Rust...? about metal grade

[Mr.Sandman]

i just bought an s13 240sx, and so far all of the actual chassis/frame is intact with no rust. Though, my only problem is, i have a 6-7 inch diameter rusted hole underneath the driver sit. The rust is only the actual flat metal sheet thats underneath the car. If anyone could help me out with what grade the metal that was used for this chassis, please i've been searching for a while now and can not find anything. Even a website of some sort that could put me in the right direction. I have a meg welder/gas, so i will also be doing some more welding on the car, and this information is crucial.

[fatboy]

i used mild grade steel to patch my rust spot.

[zippitta]

I would say that it is safe to go with mild steel...it is like the cheapest type of steel there is, and I doubt they used high grade alloys in a cheap mass produced car...lol.

If you are doubt, do a spark test.