Really? That seems very odd. Sand? I've seen my dog sit back and scootch across the lawn but sand..... LOL! Sorry but the only word that pops into my mind is chafing.
In the video you showed your food box. It looked like lots of quick easy store bought unhealthy stuff. Did you ever keep a cooler for fresher foods? I would think you would have craved veggies or meat.
You'd think chafing, but it doesn't. At least it didn't for me. The grains carry away the residual waste. Grab a little sand, wipe, repeat.
This folds up in it's own case, can hold 500 lb (on the seat, not in the bag) and with the lid closed is odorless. Height of the seat from ground level is the same as our home "porcelain appliance". I have seen reports of folks using these as a bedside commode for folks at home after a hospital stay.... We have it for use in our VW Eurovan camper. works just fine in it's own space that also is used as the 'shower' room - but not at the same time. The tailgate tent takes only a couple of minutes to set up/take down. Waste goes into a plastic bag with a neutralizing powder - just like disposing of a used paper diaper - and just as legal. In out 1971 Campmobile we used a cassette toilet. I still have it for in-home use - just in case.... http://vivawestfalia.files.wordpress.com/2006/11/69interior011.jpg the seat behind the driver ^^pic link above^^ has storage space, just right to hold the tolet while in motion, when parked, we had a side tent for use... the tent attached to the side, like this.
If this works for you, I'm sure it's awesome. We had something similar that we hauled around but it was just too big to use inside the truck and maintain privacy. For a van it would work great which was what my family originally purchased the cassette toilet for.
I was talking to someone about this thread and @avagdu's set up. The subject came up because I was talking about all the people I see living out of their cars and the cars are filled with "stuff". I think one plus regarding Avagdu's set up is that he was able to keep what was necessary and let go of the material objects. I have seen cars packed the the roof with clothes. Clothes are important but I think people keep every piece of clothing they have instead of filling that space with a cooler or something. This does happen because I spoke with a lady whose son was living in his vehicle and he did not have a cooler in there but he did have all his stuff. Maybe it is just overwhelming when you are living in your car. I know there is a difference between doing it by choice vs. having to.
Both my wife and I had small day packs with our clothes. Work uniform and a weeks worth of undergarments and three or four sets of synthetic shirts and pants for wearing off work in town. Over night and lounging in the truck we wore lightweight thermals most of the time as our "house clothing". If you choose your clothes carefully you can easily get four or five days worth of wear per piece before washing.
40 years ago I lived in a cabin in the woods that was 12 by 24 without power or running water, the best ideas and the best things I could buy all came from the RV dealers, usually used stuff. Many of the ideas on living with out power or water connected to your dwelling were perfected by the RV people to a fine art and with the changes in tech over the last 40 years, solar, led lights, good inverters, etc, it is now even better. The systems work well in any rigid wall system, cabin, trailer, van, or RV.