So i'm looking to put in a new floor pan... well mine has very little floor left to it now. but i don't know how to cut out the old one.

Any ideas what to do or use?

and also wondering what'd be best to cut things out of steel.

 

Plenty of ways to cut out the old tin. What's that old saying? "More than one way to skin a cat!" Best bet though is to get the new floor pan before you start to cut the old one out. That way you won't cut out too much and have to infill with more pieces of tin.

First choice to cut out the old one is a plasma torch. Second would be a rotary cut off wheel or grinder. Next would be a sawsall with a hacksaw blade (short). I don't think nibblers would work very well but they might. Air chisel if that's what you got. I saw a small pheumatic recriprocating saw at Princess Auto that I might get. The blade was only 2" long, looks like it might work well.