Jeff,
I looked at these a couple of weeks ago. at 4.5 feet above the trailer it could raise the center of gravity enough that tipping could be a problem depending on the width of the axel, stiffness of the springs and the rigidity of the tongue. I think I would like about 6 feet of width so I could put 4 kayaks in J racks on it. The height may allow the kayaks to go over the bed of a truck or top of a car (watch out for dips "ouch"). The height would also increase the lift needed to load them. I am thinking about using my Yakima towers on a trailer with 2 foot sides but when they are that low the trailer would need to be long. I have a big trailer that hauls 16 kayaks that I use about once a year I would like to sell it and get a utility/kayak trailer that is more practical.
Scott