I have had a Zepp on my 2003 Ultra for 5 years. I'm 6'0" and 170 lb.'s.
The Zepp works to a degree, but I also keep an Airhawk AND a Saddlemans gel pad in the trunk. On a 4 hour trip, the Zepp is enough, anything longer than that and I start switching out with the other 2 for an hour each. Also, changing leg positions on your highway pegs helps a ton. Istead of just resting your boots on the pegs, sometimes lay the back of your boot on TOP of the peg, highway peg that is.