Whups, I let this one go a little too long...
To conclude: I had zero problems driving a 17' bed Uhaul. It was a little un-nerving not being able to see directly behind, so checking the mirrors was done overtime. I kept the truck to between 55-60 mph on the interstate, and followed the posted speed limits everywhere else. When turning, care was taken to swing wide so the back end had enough clearance.
This one got about 12-13 mpg, which wasn't bad considering we packed that truck to the rooftop. Everything worked just fine, and I had no problems with the pickup or dropoff.
For insurance, I did get the full coverage. An unexpectedly kicked-up rock from a semi did make a good "thwack" against the windshield, and made my choice to get the insurance seem much wiser. With my luck, that rock would have cracked the windshield if the insurance had been skipped!