Steel bed cross sill replacement

[i82much]

What's involved in replacing a few rotted cross sills on a 72 longbed with a steel floor? Is this something you can do without removing the bed?

My floor is pretty rotted in one section and has a couple of bad supports under it. I'd like to be able to repair the supports and then just lay some diamond plate over the rotted floor to give me a few years of functionality. Not looking to make a lifelong repair.