Using the three-strap setup, I've gotten away with a 2,000-mile round trip from California to Wyoming (no problems, in other words). A lot of high speeds--the limit through Nevada at the time was 75 mph including big rigs (some of it was 80 mph this year) and that's what everybody did--but no bumpy surfaces except for the occasional road work-related pavement change.
I've also gotten away with towing the boat to Tahoe several times, a much shorter trip on sometimes dodgy pavement.
I tighten the strap ratchets just short of the point where the hull flexes.The aft and center straps have always worked fine, but the forward one had a tendency to work loose until I finally figured out how to place it.
GreenLake, I've thought about separate attachments on each side, and I do like the idea, but I can't figure out how to create guaranteed strong points on the boat without major surgery that I don't have time for, so I'll go with this for now.
If I lose the boat off the trailer, I may or may not tell anyone.