Hi everyone - I am looking to assemble the bed to my truck (I didnt disassemble it). Am I right that there are only 2 mid-cross braces that hold the box to the frame + the rear cros brace right under the tailgate? I see some ads where 3 mid braces are for sale. Are the sets of 3 for the long boxes?

Also, is it possible to mount the bed securely to the truck without the floor to ease sanding/prep of the panels? Thanks!!!