I have a 1875 crossover and I was not happy with the holders that slide into the inside rail . There are two types of them .
one type wraps then gets screwed to the out side out side of the haul .But this is a very high system and is hard on the boat cover. I talked to one of the tecks at lund I went with what he told me he does.
On the under side of the side rail I glued a piece 3/4 inch wood in ,to give it more straight about 15 inches long . on top I screw apiece of plastic deck boarding or you can use wood and on top of that I screw my Scotty electric mount to that . I run 15 lb balls and she is strong. i can post a picture later if you want.