Why shouldn't it show that? If you move the dang spool out o' the way you can see the trailer frame. They're not hidden lines, they're visible phantom lines.
Fine... If you don't want to see those parts in your alternate position, just go to the assembly and hide them in the config that is referenced by the alternate position. Or, stay in the drawing and find them in the feature tree under the alternate position view and hide 'em from there.
If your trailer frame is just one piece, and you can't hide it, go to the assembly and make an assembly cut that is suppressed in the main config but unsuppressed in the alternate position view configs.