Not really. If you don't make a complete mess of it by driving around with the windows down on the playa, it's not that big of a deal. My washing routine went like this:
1. Sweep out the inside of the box completely
2. Pressure wash and brush the outside of the truck entirely and pressure wash out the floor of the inside of the box
3. Vacuum the inside of the cab
4. Do a full pre-lim wipe down of the inside of the cab with soapy rags and/or baby wipes
5. Do a final wipe down of the inside of the cab with vinegar/water and paper towels.. making sure to throw the paper towel away after each small section as to not wipe playa dust grime back over the surfaces again..
That last one is the trick. Get an entire roll of cheap paper towels and go through just about all of them. If you don't keep throwing out the towel, you'll just keep wiping dust back over everything. All in all, it takes about an hour of solid, focused work.
Or.. you say to heck with it and negotiate with the guys on the spot when returning it and see what kind of deal they'll give you. You can always say no and drive down the street to a car wash and wash it.. at which point when you go to drive away, they'll make a final offer. Bargaining skills help here..