I've found that trailer speed really depends on how the trailer is balanced and how much it weights. With a full 12' Uhaul, which probably weights about the same as a 986, I normally average around 60mph. It's not worth going faster, especially downhill. I also would NOT try and cover your 986, flapping fabric will do more damage to the paint than a few rocks. You might look into temporary clear bra, or even masking tape.
I'm glad you are planning take it slow and I hope your move goes well!
