Battery drains flat over night

I would suspect you have a bad Totally Integrated Power Module, the fuel relay is a common fault on them as on many other Chrysler products as well. The relay fails with the contacts welded on and removing the fuse stops the power from going to the pump.
There are a few companies that offer relay bypass kits for them and they are actually very easy to install if the relay is the issue.

I prefer to add a new better relay like a 30 amp Bosch style unit and just re-route the OEM wiring to control it, that just removes the OEM relay and makes the system better overall.
This is so common that Chrysler offers kits to do the bypass, but you can do it without the kit which uses a light duty relay.
If you wish to do the bypass you need a relay with a socket similar to the ones shown. Then you need to look at the wiring that goes into the TIPM. You will need to find the fuel pump control wire, that is a Brown wire that goes into connector 1 pin 40 under the TIPM, Next you need the power feed to the fuel pump itself, That is a Dark Blue wire with an orange stripe that comes out of pin 10 in connector 5 under the TIPM.
Now you need to mount the relay in an area where you can reach it with those 2 wires. Then you will need an inline fuse holder to fit the fuse from M25. You will also need a ring terminal that fits the stud on the TIPM as that will be where you draw power from.
The ring terminal will attach to two of the wires on the relay socket, those go to pins 30 and 86 on the relay and provide power. Then you take the inline fuse and connect it to the wire that goes to terminal 87 on the relay. The other end gets connected to the dark blue wire with orange stripe from the TIPM harness, it will provide power to the pump from the relay.
Then you connect the wire from pin 85 on the relay to the Brown control wire that grounds the relay and turns the pump on and off. With everything connected the pump should operate properly for a long time.

This site shows the process with the OE kit but the kit gets wired in a bit different, and depends on another light duty relay in the TIPM to do the switching.
https://us.autologic.com/news/chrysler-total-integrated-power-module-tipm-fuel-pump-circuit-failure

OH and in the event you wonder why I'm giving you information to fix a VW but using Chrysler a lot, the Routan is actually nothing more than a Chrysler Town and Country or Dodge Grand Caravan that VW had trimmed out for themselves. Unfortunately they kept much of the wiring and chassis and inherited the TIPM issue as well. Chrysler had a recall on their vehicles for this but only certain ones and VW did nothing.