Disclaimer: I have no trade qualifications of any description at all, I'm sure there are better ways to do the following, but this is how i did it using what tools i had available 
Ok so i was asked to explain in detail how i did the floor in my cruiser. Well i,m a one finger typer so that would take me a year. by the time i get half way through typing something i have forgotten what it is i was going to say
Anyway so i took pictures of how i did it. but you will laugh when you see how
very low tech here.
The reason for the request
Now keep in mind that i did this fairly quickly so is a bit rough
Tools i used. With a bit of imagination I'm sure you could come up with better options. i just use what I've got
I started by making a templates of the desired shape, one for the inner edge and one for the outer.
using the smaller template mark out your steel, Then i go around the end curve with a screw driver giving it a good firm whack with the hammer. Do this on a piece of carpet so there is a bit of give under the steel. the piece of carpet I'm using is folded in half to make it a bit thicker
Then go up the sides, i use an old wood chisel for this or a brick bolster. you may need to go up each side a couple of times just to get things even
and you should end up with something like this
Next bit is a bit hard to explain.
turn the steel over so that the indentation is up (like in previous pic) This is where the lines on the templates come in handy.
Lay the small template back on the steel and mark lines on the steel in the the same place as the ones on the template. Like so
This is just to help line up the larger template

Ok so i was asked to explain in detail how i did the floor in my cruiser. Well i,m a one finger typer so that would take me a year. by the time i get half way through typing something i have forgotten what it is i was going to say

Anyway so i took pictures of how i did it. but you will laugh when you see how

The reason for the request

Now keep in mind that i did this fairly quickly so is a bit rough
Tools i used. With a bit of imagination I'm sure you could come up with better options. i just use what I've got

I started by making a templates of the desired shape, one for the inner edge and one for the outer.

using the smaller template mark out your steel, Then i go around the end curve with a screw driver giving it a good firm whack with the hammer. Do this on a piece of carpet so there is a bit of give under the steel. the piece of carpet I'm using is folded in half to make it a bit thicker

Then go up the sides, i use an old wood chisel for this or a brick bolster. you may need to go up each side a couple of times just to get things even

and you should end up with something like this

Next bit is a bit hard to explain.
turn the steel over so that the indentation is up (like in previous pic) This is where the lines on the templates come in handy.
Lay the small template back on the steel and mark lines on the steel in the the same place as the ones on the template. Like so

This is just to help line up the larger template