To get directly to the chase...
The Mrs. has said that without a proper INDOOR biffy/loo--which means NOT having to get out into the elements to address bodily necessities, the notion of a TD is DOA. So, the build begins at the end so to speak. As a matter of practicality the inclusion of such a feature imposes some design problems. I have thought about this and have reached the following conclusions based on emperical observations...
First, I simply cannot fit a biffy/loo in a 8' trailer and still have room for a bed AND a decent hatch for a kitchen. So, first conclusion is that this will be a 5x10 not a 5x8.
Based on real life measurements (don't ask) your standard biffy is about 16 inches high. The good news is that porta potties are near that and a simple platform can raise them to that height if they are a bit short. In the act of using this item one's head is approximately 48" off the floor if you are about 5' 7' and higher if you are taller. So, a 4' sidewall with a curve at the front would be somewhat short of satisfactory. Which seems to mean that a 5'sidewall will be the order of the day.
Placement of the porta potti would be in the front corner, in an enclosed cabinet with a liftable cover which would have a latch on the wall to hold it up. The potty is about 16" square. The space between the potty and the opposite wall would be empty, permitting the users legs to extend while using same.
Now, the bed would be about 76 " long but the end of the bed would be just about an inch shy of the porta potty and extend to the rear of the cabin a total of about 76". The doors would be moved further toward the back to allow for the placement of the bed toward the rear. The Foot of the bed would be the end closest to the loo/biffy (for obvious reasons).
By placing the head of the bed toward the rear, the configuration of the cabin must change. The rear must be more of a 'Boxster' than a streamline shape. In shjort, it must be more of a rectangle than the typically curved hatch. I estimate having room for a kitchen layout of about 2' deep at the rear, which limits what we can do with that but there ARE tradeoffs in this stuff, no?
I would probably have an external door to allow removal and servicing of the porta potti.
Now, does this sound insane? Ok, it does, but does it sound doable. Have any of you used porta potties for camping and are they satisfactory for the kind of night time use (primary use) or occassional road side emergency? I have tried to convince the better half to that a bumper dumper might be a reasonable choice but INDOORS is non-negotiable.
A disposition to preserve, and an ability to improve, taken together, would be my standard of a statesman...
But what is liberty without wisdom, and without virtue? It is the greatest of all possible evils; for it is folly, vice, and madness, without tuition or restraint.