I actually just finished a reread of the original 6 Dune novels earlier this year and read a few interviews at the time where him where he mentioned the car repair manuals!
I have several of the BH/KJA novels that I've picked up at library sales, but haven't found the will to read them yet. (I have a very strong dislike of KJA from some of his previous work.)
One of my high school English teachers was a huge Dune fan and was the main reason that I picked up the books a few years later.
I only have the first three in various paperbacks, but I do have the signed/limited first editions of 4, 5 and 6.