The roof is not UHMW it's just polyurethane. I'm not worried about scratching but have you actually seen the plastic roof attachment brackets? I was thinking of making some tube clamps with supports that would protrude through the roof and accept standard rectangular roof racks but I would like to hear from others who have attempted to make a Rack. Suggestions of a trailer, a pad on roof, or just strapping it on while humorous does not address the question. JMHO
You may think that my response to your question was humorous but I'm being serious. I was giving you a much more simple option in my opinion. I was truly trying to help. If I were wanting to carry a small lightweight boat into the woods, I would most definitely strap it to the roof. My reasons are because it would save me time from not having to make or purchase a roof rack, it would save me money for not having to purchase a roof rack or buy the materials to build one, I don't want something permanently mounted to my roof that will affect the center of gravity and have a negative affect on the vehicle's performance at high-speed's or off camber situations and lastly my experience tells me that the OEM Honda roof will take a lot of abuse and holding a 70 pound boat will be no problem. I've carried lumber from my barn to a place for we were building deer stands and equipment sheds and put 8 4 x 4 posts on the roof and I don't just gently put them up there either.
I do understand that we don't all share the same opinions so if you would like to seek a permanent structure added to your roof then certainly feel free to do so and I'm sure someone else will be along to help you as I do not have any experience doing that with this vehicle.
One other thing, what roof do you have? I thought you had the Honda roof. Who makes a polyurethane roof? I know the Honda OEM is UHMW polyethylene. At least mine is because it has a stamp on the underside that says so.
It will at least hold me! I weigh twice as much as that boat....