Building a 20' dump bed, should it have a positive camber built into it?

They're built level.

 

Are you building your own dump body?
I think that would be a huge project to take on, hopefully you have a good shop set up for that project.
Also pretty curious on the specs and intended usage for a truck that's getting a 20' box.

I just put a brand new dump body on my 2000 truck last fall. They are pretty spendy, by the time I had the FET figured in I was north of 40k, but I tell you what it was some of the best 40K I have spent in trucking.

 

Not trying to be a complete negative Nancy, without getting out my build sheet or quotes from other outfits, it seems like you're on the right track, and I admire your ambition.

You may want to look at lining the sides and tailgate with either plywood or UHMW, it will keep your box looking much better for much longer, but leave that floor steel!
Also a high lift tailgate comes in so handy, I would have to be in a very penny pinching mood to order a dump body without. If you're building your own it's a no brainer to put it on, unless you are strictly going to be hauling light aggregate.

And to answer your original question, Flat.

 

What brand body did you have installed?

 

I have never seen a dump body that wasn't level to the frame.
This is a interesting thread, and a great deal of work for someone, i hope you do well with it!
Please post pictures as you proceed.

 

Will that truck do very little miles in a year?