I just picked up a Cuda from ARC yesterday and started my rigging with a transducer mount. I have a Garmin Echo 300c to mount up. I basically took one of the scupper plugs that came with the yak, cut some strips of 16 guage aluminim for mounting arms and here is what I have so far...
I used a hammer and beat the aluminum to round out the top to the shape of the scupper once it's pushed down into the hole, drilled some holes about halfway down the scupper, put a washer on the inside and used a pop rivet to hold it all in place..

Jackson Kayak Cuda Transducer Mount
From the top...

Jackson Kayak Cuda Transducer Mount
From the bottom...

Jackson Kayak Cuda Transducer Mount
It was at this point my camera phone died, so I will take more pics soon of the actual transducer mounted. All I did was place the transducer into the recessed scupper hole about even with the bottom of the boat, mark holes for the bolt and then mounted it up. To make sure I get the best signal I may need to move the transducer up or down so I left some extra metal on the end and drilled another set of holes above and below the middle set so I can move it easily. Drill a hole in the bottom of the scupper for the wire and it's good to go.
Tom