I finally pulled the trigger and picked up a Garmin 546s with transducer. It arrived yesterday so I can install it tonight/tomorrow. I was checking out where to mount it and trying to figure out a way to do it.
The base has a circle that you run 3 #8 screws through. Since I have no flat service in the Helm (the newer Horizon's have a cup holder to the left of the gauges where they mount, but mine does not have that), I was trying to figure out a way to make a flat surface. I found some flat rectangle and "T" shaped metal (roofing dept at Home Depot) that would work. I originally searched for the mounts they make for cars to hold your cell phone that slip between the dash trim and plastic, but none seemed the right shape.
I was trying to avoid drilling any holes in the flat dash surface just to the right of gauges which I could screw a "L" shaped piece of metal.
I was able to slide something in between the dash lip, but not sure how to secure it behind (need to pull the radio to see up and behind there.
Does anyone have any ideas? The unit fits perfectly in that corner with the bottom of the frame on the right of the Garmin resting just above the tan cushion in the middle of the red arrow and the other side just right of the trim gauge.
Thanks for any ideas.

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2010 Sea Hunt Triton 220 "Big Whiskey"2003 FW Freedom 180 Volvo Penta 4.3GL/SX-M "It'll Do Four Now" (Sold)
2012 Avalanche LTZ 4X4 