Here is what I did. I got a diamond mount for the rail and put the FF there and then put a RAM revolution in the middle spot. I also have the "tub" also. I used cut outs from an old ("Honey have you seen the cutting board") cutting board as backing for strength. I run the fishfinder off rechargeable AA batteries and keep them in a small drybag. I mounted the transducer in goop and have had no problem.
Hope this helps
Mike
