Design suggestion needed - simple plastic slider for small boat transducer

Hi.  I need to add a small sonar transducer (fishfinder sensor - small 2"x3"x3") to the transom of a kayak.  The transom is the flat backwards facing keel-like appendage in this picture.  It is ~3" wide and a foot vertical.  There is a hole in the hull directly above it, so it can be accessed from above.

This shows the kayak transom http://i960.photobucket.com/albums/ae87/nickmdal/Bassyaks%20photos/IMG_4068Medium_zps318a10df.jpg

The transducer  needs to be able to slide up 2 1/2", so that it won't get dinged when transporting the kayak.  Therefore I want to attach it to something that I can slide up, but will remain attached to the transom.

Envision something like a paint stir-er flat against the transom in a vertical orientation.  From above, I can grab the top and pull up to raise the transducer.

I am imagining the transducer's "holder" to be some sort of rail/guide combo that is friction and not wheel based.  I found these items, but nothing any more useful.

http://www.soucyplastiques.com/en-CA/_media/image/big-glissiere.jpg

Other thoughts were drawer center rail siders, tie/belt sliders (a hacked one).  That and the pic above are all I could think of.  Any suggestions would be so appreciated.