Wall and Floor attachment to trailer?

I have a 5x10 trailer that is currently being welded together. I'm getting my plans together to attach the floor to the trailer. I've seen this illustration on the different methods of attachment to the frame:

My plan is to use the simple Lap Joint. My question is, what would be the problem of leaving out the 2x2s under the floor? Would I run into any problems by bolting the floor and the walls directly to the metal trailer frame?
Thanks
My plan is to use the simple Lap Joint. My question is, what would be the problem of leaving out the 2x2s under the floor? Would I run into any problems by bolting the floor and the walls directly to the metal trailer frame?
Thanks