Modifying Trailer Shell Size
It has been done before but it is a tremendous amount of work. There is more to the task than simply shortening the shell and frame. Remember balance and proportioning are two big factors that come into play, so this often requires shortening both ends rather than one if you want to end up with a normal looking, towable rig. This gets more complicated when a rear bath is involved.
I would suggest pursuing a smaller rig if that is your ultimate goal.
"You wouldn't worry so much about what others think of you if you realized how seldom they do."