Before my father died in August of 1972, he bought his very first brand new Chevy pick up truck in the month of June and put a cab in the back to ready for our family trip to Florida (and room for 4 kids not all squished in the backseat of the sedan) He had made bunk bed that slid from single to double size (this was a tall cab) and made a box for the 'potty'. Ken's mod made me think of it, and I hadn't in years!!
It was a re-enforced plywood box with woodgrain sides along with what I remember to be a thick (probably 3/4 plywood) painted seat that you completely removed (not hinged, it was braced on 4 sides) to empty (no solids allowed!!) and a regular ol' 'bucket' was inside. He also put a hinged padded top so it could double as a seat when not used as a 'potty'. This made for more streamlined traveling with his 4 daughters!!
I can still remember riding down the road (I was 9 at the time) and asking my mother in the truck cab (via the intercom from the front cab to the back cab) if I could use the 'potty' and her saying "Yes, just make sure the people behind us can't see you!" (there was rear door on the cab with frilly curtains). This was before I-75 went straight thru, so we had to wander thru the Smokey Mountains (not by-passing them like we do now!) and stayed the night at road side parks. My parents slept on the hard truck-bed floor, while the daughters (aged 9-15) slept in the beds.
That was the last time we went camping as a family...and probably the last time I went 'potty' in a bucket, but it was a dressed up bucket!
Just thought someone would be interested in my dad's porta-potty/bucket modification.