Have the Roo 19, love it. We've even done ~3 weeks with 6 adult-sized folks (Ma, Pa, 3x Teens +teen girlfriend (son's, not mine!)) through the Canadian Rockies. However, when loaded down with all people and gear, I was 700# over GCWR. I went ahead because all axles were below GAWR. I don't know what the "80%" rule is. I went with the hard documented vehicle capabilities and accounted for every pound. Make sure you pay attention to the math. It's usually not a matter of pulling the load; STOPPING the load on a steep grade is the point where you take your life into your hands. No shortcuts on weight ratings; use the scales; tune the weight distributing hitch.
Hat tip to BIKENDAN, he taught me all of the above.
