As a former dealer, I use to instruct my customers electronics is fine but when too much emphasis is placed on them at times I saw when my customers were spending too much time on them instead of looking around and forward would have grounded and/or hit other boats/people and so on.
Best advice, ask the locals, not the weekend warriors, for the local knowledge and have a chart with you so any issues can be pointed out. Never sail/motor at night unless you know the waters well. As for inland lakes, depth is easy most of the time to tell. If there is an island, shoreline, look at the elevation how the land lays. If steep at the shoreline, you have a good depth but if shallow, think of that with the land extending out from shore with a minimal depth for some distance. True with an island as well.
Too often I saw folks rely too much on electronics. Here is a good scenario. What if you crossed over the Chesapeake Bay Bridge Tunnel at the entrance to the Chesapeake Bay from the Atlantic Ocean at dusk about a mile or two past that, fog sets in and all of a sudden your electrical goes out along with the electronics and it is itch black. I always taught my customers as a back up to carry an AM Radio, flashlight and local charts and/or state highway road map with them knowing where the major AM stations are broadcasting from. Turn the radio until you have the strongest reception from two if not more stations and crossplot that on a map. It works and it used to be called RDF in the old days. This actually happened to me and I was able to come within 500 feet of Willoughby Spit at Norfolk next to NOB(Naval Operations Base) in the fog all the way. But in this case, we are dealing with a lake. Still applies
Most sailors as a good example will not run the Dismal swamp canal nor the Alligator River ICW at night. I did once at the behest of the owner on a Catalina 387 on the Alligator River ICW at night and it took everything out of two experienced sailors just to navigate that. I did it once and will never do it again.
As for attaching a depth sounder to the hull, Kermit made me a believer that plumbers putty does work. Kermit advise on that if you are reading this. I find it easier than epoxy, mineral bath solutions, and so on. The key to that is to prep and clean any surface and when inserted, insure there are no air bubbles. Give it time to set up