Has anyone tried these kind of slick plastic bunk end covers? They are supposed to protect the high wear area at the end of the trailer bunks and also help loading and unloading the boat at the ramp.

I've seen them, haven't tried them, but they look like a good idea.  A few years ago, I went with the ultimate bunk boards, so they are unnecessary for me now.

Not sure about the "end covers" but I have some cheap plastic slicks on one of my trailers and they are fantastic!  Barely have to put the trailer in the water to load or unload my 16ft Alumacraft bassboat.  Bought another set to put on my tracker flatbottom trailer one of these days.  Just make sure the winch strap is attached and locked down when you go up or down the ramp if you don't want your boat sitting on the ground.