I used the duct seal method to mount my Garmin Striker 4+ transducer to the inside hull of my Pelican Catch kayak. It worked great initially but has come loose a couple times. I press it back in place and the duct seal seems tacky enough to hold it again, but has come loose more than once. Is this normal?

 

I did make sure the spot was clean. Seems to happen in colder weather. Any suggestions?

I don't use that method with my kayak but I'd think anything using an adhesive type attachment to plastic is going to have issues in the cold. 

Try Gorilla tape.  It's the best duct style tape I've tried.  Though nothing is going to stick to plastic well in a wet environment, especially in cold temperatures.  Even worse so if it's trying to hold something heavy in place (like heavier than the tape itself).  Most plastic kayaks are made of HDPE, which has a very low surface energy.  So adhesives of any kind won't stick to it well.  You can try to rough up the surface, but your best bet is to mount it with hardware, or find a way to plastic weld a solid mount in place.  

What about a homogeneous glop of silicon?  You can peel it off easily of each component if you care to pull the plug. 

Have you tried using a pool noodle?  Cut the noodle (make it a snug fit) to hold the transducer, use marine goop/glue to secure the pool noodle, press the transducer in the hole.  Also, make sure to use to clean the place for the noodle using fine grit sand paper and and alcohol.