In another post I said that we used to carry a Wastemaster cassette and the water roller tank in the shower/toilet area when on the road.
I had had problems with the cycle rack we were using and decided to replace it with a tow bar mounted rack similar to the Thule. A cheaper copy is made in the EU and I managed to source one in Poland, straight from the manufacturer. I went for the two bike version, as we only normally carried two bikes. In the event, the company sent the more expensive three bike version by mistake, for the two bike version price. It was not worth sending it back for the correct one due to the costs involved; also, I had an idea.
I did not fit the upright and plastic fittings for the bike rack closest to the van and planned to mount our bikes outboard of that space. I purchased a metal aluminium tool box and bolted it down onto the bike carrier in the centre over the tow bar. We now have some additional storage on the back of the van and the Wastemaster cassette and the water roller tank are stowed on top of the tool box. The bikes are outboard of that. The bonus is that the bathroom is now instantly available when on the road. A definite plus.