I would not like to trust a pressure reducer. Even if they are successful in reducing the pressure, are they fail safe.
But even using a float valve in an Aquaroll, if there is a failure with a joint or pipe in the van, a lot of damage can be caused in a short amount of time.
At least filling the tank up each time limits the total quantity of water possible to flood the van.
Most vans have the pump on/off switch near the door. So it is best to turn it off every time we leave the van or go to bed. And if using a pressure reducer to turn the tap off each time.
Do I do that. No, life is too short.
As an alternative, I know of someone who has fitted a float valve into a 1 gallon container. Works just the same, but difficult to get it to sit still under its own weight. Perhaps it could be strapped to the wheel. Aquaroll for me, x 2.
John