I have been collecting Costco kitty litter plastic containers. In your case, I might suggest you build a frame that would contain the plastic containers on their side, stacked, with the tops cut off so you can load up the space.
The construction of your framework should allow for the bottom container to slide out, and a different container can then be added onto the top, sort of like a beverage dispenser in a fridge.
If you need to have something to hold things in, get some stretchy flat elastic material, and fasten it partly across the opening with some pop rivets.
Build the same framework at another place in your van, and then just pull the container out of one spot and put it into the other spot as you need things.