Ugh...I think I need some suggestions

Hey Guys,
Now the excitement of the new trailer is growing thin, I took a long, hard look at the frame of the new trailer and think the welder may have made a boo boo.
It's a big thing and I should have noticed it since it's so blatantly obvious but he used aluminum angle for the trailer rails instead of c-channel which would have given the desired flat top to lay my floor. The angle is not going to lend itself to installing the floor so that the side walls hang over the sides of the trailer. Am I screwed? How can I build it so that I can over-hang the walls? I have made more mistakes than I can count in my building efforts but this is the biggest.
Any ideas as to how I can change my design?

Now the excitement of the new trailer is growing thin, I took a long, hard look at the frame of the new trailer and think the welder may have made a boo boo.

Any ideas as to how I can change my design?
