Well, for anyone whose interested, the harness does fit in the Fleetwood. Or at least mine did. Mine measured 18' long. I ran it from the fuel pump connector up and over the gas tank, through the clip for the fuel lines, over the brace above the axle, then into and along the frame rail and then exiting out the frame rail hole near the passeger front inner fender. I had enough wire to go along the inner fender and connect directly to the alternator post.
The fourth wire that the Fleetwoods have is another ground wire so I bought 1 complete 4 wire weatherpak connector(1 male and 1 female) to replace the 3 wire connectors that you get on the Racetronix harness and ran a jumper wire between the D(fourth) sockets. Now it's truly plug and play and works like it should.