My potty is the Camco 41541 5.3 Gallon model.
http://www.amazon.com/gp/product/B004SFKJIQ?psc=1&redirect=true&ref_=oh_aui_detailpage_o03_s00
The product I put in the tank is called "Pot Shot". It's a non-formaldehyde, biodegradable deodorant designed for buses, portable toilets, RV's, trains and boats. I found it when I was driving corporate coaches/buses for Apple.
Personally I don't think I really need it for odor control. The sealed, sliding valve on the holding tank doesn't leak a drop or let even a tiny amount of smell out of the tank when it's closed. The product is said to be "Equipment Safe", and so far it hasn't eroded the seal at all. I don't use very much of it though, given my holding tank is nowhere near the size of that found on a train or bus.
Interior room is almost nonexistent inside the TC, so the toilet sits right next to the bed. When I'm watching movies, and facing the other way on the bed, the potty is right next to my arm. I actually use it as a table to put my snacks and tea/cocoa on while I'm watching a DVD, and I don't smell a thing.. not even the deodorant. Still, having to remove the top tank and dump the smelly, stinky mix of poop and water into a flush toilet or dump station, isn't something I look forward to.
My reason for considering the bucket design is because of the limited room inside the van. If I use both the bucket and a potty, I'm using up the already limited room I have to work with just storing the both of them. If, on the other hand, I used just the bucket, I'd have more room for other things, like my feet.
As for why I mention the 7 gallon design... I'm 6'4" and find a 5 gallon bucket to be too short for my long legs and often sore lower back (I'm going to be 50 next week).
I know I could add legs or a block of wood under a smaller bucket, but that would just be more "stuff" to carry around.
