>>> some kind of pocket glued on to the trim tab that you just push the transducer into perhaps?
Now that's a really good idea. Until this year when I bought my old Aerotec to refurb I had no experience of patches/gluing etc but now I realise with a little care you can make a totally pro looking job.
There are loads of PVC backed fittings available for SIBs and I'm sure one of them could form the basis of a mount.
There are loads of possibilities on this page...
Ron Hale Marine Ltd - Inflatable Boat Spares and Accessories