I personally prefer rail, side, rear... mount whatever
(no glueing!) -
my reason for doing this - I can change where it is placed - whenever i want & upgrade or change something out w/o leaving messy-ness. I also use my fish-finder on multiple kayaks & a porta-bote - so by having it on a mount I just move it from one to the next.
I use a lowrance 4xDSI - depending on my type of fishing i'll change the position. For crappie I'll mount it off the side up front. When i'm trolling for sandies - I'll mount it off my crate in the back. For nicer models that type of positioning might not be as big of a deal... but i find the option to make those changes nice