We have an Avan Cruiser which is only 12ft long inside but we can carry a porta potti in one of those zip up canvas bags under the (tiny) table at the front of our van. It sits there when travelling or parked in a caravan park where we do not need to use it. The canvas bag disguises it and makes it easy to carry outside when you want to use it. It does not move around on the floor so there is no problem and there is absolutely no smell from it whether dry or half full. Then we have a pop-up ensuite and the porta potti goes in there when stopped at a bush camp. Easy, simple and convenient. Use the Woolies nappy wash and Bob's your uncle.
Good Luck.

We have a 14 ft van with a cupboard under the wardrobe between the single beds, we put ours in there while travelling and for storage. During the night we put it out up close to the front of the van.
We had to buy a smaller one in height to fit in the cupboard but I just made a collapsible stand that folds flat to make it a good height to sit on.
Same as Hako we use Nappy San equivalent as long as it has 30+ % of sodium per carbonate , no smells .
Wouldn't be without it!
If your van has a double bed some already have a door on them , or it would be easy to modify.
Jetta

Thank you so much..we honestly had no idea. I had seen some in cupboards when browsing on websites but most do not even mention it. All so much clearer now.

Once again thank you! Not long to go now!

Happy days!