Make a quick model that worked really well and have made even more for people at the campground. Fits into the top of the white plastic trailer poles to help guide you boat on, print in a flourecent bright color to make even more visable. Worked great for a pole that is 2" inner diameter, but could easily scale for different sizes. I used a dab of silicone as a set screw to secure (away for part that could touch boat) Then I also drilled a hole in the plastic right below the guide to allow air to escape as you back trailer into lake.

Very Quick and easy print - much better than the cheap white plastic caps that come with the sets of guides.