My two cents is leave it alone. Who cares if it drys out its under the V Berth locker in an almost inaccessible area for storage in a boat with no bilge. If it drys out and still works; great that just means it's easier to clean up when the transducer fails. I have had plumbers putty on my transducer for 2 years now with no issues and others have had it much longer. If you epoxy it in place you will be grinding or cutting it loose when it fails. Its only a 22 foot boat and it only needs 2 feet of water anyway so the depth is more of a luxury.Plumbers putty is a good temporary solution. Problem is “It drys out” once out of the sealed plastic container.
Once you have found a good location you need to look at using materials that are more permanent.