Don,
I did 1015 miles on a 24 hour rental of a Road Glide Ultra last year. Yes, the dealer was quite surprised. However, at 70 to 75 mph, I was getting about 44 mpg IIRC.
If you have an Airhawk, take it with you. You will need it for your tailbone (assuming you still have the stock seat). You may want to also take some beads and a sheepskin. I used all 3 at different times on my run.
I was pleasantly surprised with the road manners of the HD. Handled nicely and had plenty of power. The 6th gear only seems to come into play after about 70 mph. It causes vibrations below that. Don't think I would ever own one though. But, we shall see. Lots of riding years left - I hope.
I did not turn in any paperwork for this Harley run. Got enough certificates on the wall.
RR