I'm of the skeptical category also. I doubt they would be very secure during travel. On my former trailer, I would clip a wooden clothes pin on the end of each gutter downspout. This would extend the distance away from the trailer the line of fall of water run off out of the gutter. I know, more redneck engineering,
but it was what $.02 per downspout? Over the course of time, all gutters need to be cleaned out, with all the chaulky gunk that drains off the roof. With an old toothbrush and a mixture of bleach/water/elbow grease, you'll be good to go!