I wouldn't bother with the swiveling feature, as it seems more likely to fail than to be useful. It also forces the wheel to be small in diameter, so it won't roll well.
If the same point on the trailer (rear bumper?) always hits first, then well-placed wheels (or just skids) seem like a good idea to me. My motorhome (which has the same long-overhang issue as a trailer) doesn't have any, but a neighbor's motorhome with a much lower-mounted hitch on the back does have skids at the hitch mounting points - each unit has what suits it.
A larger wheel makes more sense to me. Rather than the swiveling wheel or the mini-rollers below
the frame, I would rather run a bolt horizontally through the frame as an axle for a much larger wheel positioned right beside
the frame (and of course projecting down a suitable amount). For instance a hand truck wheel
(with a solid rubber "tire") could go onto the frame just ahead of bumper, protruding above the top of the 3" tall frame and further below it.
Regardless of the wheel or skid design, I think anything like this should hang down only barely below the clearance line of the trailer, so it doesn't cause more problems than it solves. That would normally mean mounting it well ahead of the rear face of the bumper, if it hangs down from the frame significantly.