I am surprised the DVD XCopy, DVD Shrink, DVD2One, Clone DVD, DVD Ghost or Sly Soft's Any DVD would not copy it. All reduce dual layer DVDs (via compression)to a single layer disc. There are also utilities that identify the copy protection scheme so that you know what you are dealing with. Again, if this is for archival purposes, you are within boundaries. Parents do this with their kids' DVDs which often have a variety of food particles before the kids use them as Frisbees.
That said, the RB1 may not be able to read DVD+- R/RW. Many car/SUV players do not.