Couple questions on rigging the FF

DO NOT forget the Marine GOOP

Yes, very important.  Everyone who has a fishing kayak should have a bottle of this stuff just lying around. 

If you happen to forget it though, I believe Nestucca Valley Sporting Goods carries it in your neck o' the woods.

While my method might not be too pretty it was very effective for my T-13...

I used the transducer that came with the FF. Turned the yak upside-down and placed it where I wanted it to be. Taped it in place with masking tape. Turned the yak back over and put epoxy around the transducer. Be sure to leave a hole to allow water to drain around it. Works like a champ. It has been in place for two years and I land on the beach and put the yak in the back of my truck with no problems. It looks like a little plug in the hole.

The epoxy is probably an inch or so thick.

Fairly easy and effective.

 2. the t13 has a transducer scupper. how far does a transducer hang below the hull?

The proper transducer fits into the hollow molded into the hull.  The transducer does not hang down at all.
http://www.demonick.com/kayak/FF.GPS/transducer.html

3. other than having to drill for the scupper mount. which has the advantage?

No need to drill a hole for the transducer cable.  You can coil up and tie-wrap the excess cable and put the coil in the sonar shield.  Use the sonar shield drains to route the cable.
http://www.demonick.com/kayak/FF.GPS/mount.html