The 5200 worked very well on my transducer wet mount. I managed to get a relatively neat bead completely around the bottom of my mount without getting the sticky white crap all over things like I did in the past. I let it cure for about a week (it rained all week, so there was nothing to lose by waiting). As far as I could tell, the 5200 made a perfect seal with the hull. I had roughed up the hull with sandpaper and it adhered well. For this type of application I think that 5200 is superior.
BTW: While the 5200 worked great, I didn't get enough Goop on the side seams to get a really good seal. The second time out, I dropped the kayak getting it off the truck and I popped one of the seams. It wasn't a big leak, but my transducer was nearly uncovered by the time I got ready to launch. I had adequate sonar performance most of the time I was on the water, but my readings were a little spotty when I was rocking in the swells. I said when I started making the wet well that I would only give it one chance and would tear it out if it wasn't perfect. Well, it got two chances and I had to get rid of it. I could have tried Gooping all the seams again, but that would have been a pain in the ass with no guarantee of success. I was eager to get back out to fish the next day so I pulled the whole thing and went with a Goop-to-the-hull mount. Either I did a better Goop job that I've ever done before or I just selected a better location. The Goop mount is giving me very good readings. I was metering the canyon down to 583ft in 200khz. I'm not going to bother with a through hull until I have to replace my head unit (Lowrance LMS 527C DG iGPS). That unit is no longer in production and the best price I can get for a compatible thru-hull is $394.
http://www.lei-extras.com/store/sear...ProdNum=106-79
If I move up to a Lowrance HDS FF I'll spend the money for a thru-hull.