For the transducer you could get a bracket welded so that the holes are in it and not the hull. I had to change transducers myself and of course the new holes didnt match up, so I used a piece of 10mm ally I had and screwed it to the hull using the existing holes with plenty of sika flex. The 10mm ally I drilled and tapped to take the new hole pattern.
I've used those tidy clips but have had trouble getting them to stick, maybe there is a Marinised version. I did have some HD double sided tape which seems to hold but first I had to clean the area with ally cleaner really well.