I had this unit in my last boat, and I loved it:
https://www.fusionentertainment.com/marine/products/stereo-units/ms-ra70n
It's fairly priced, allows for Bluetooth connectivity, it's small, and it's made for marine applications.
When I switched boats, I decided to go with a waterproof Bluetooth speaker from Braven, and it works well.
I consider myself a somewhat grumpy, somewhat old man, and I like the sounds of nature when I'm fishing. I still wonder why everyone decides to interject their opinions, rather than just providing answers to posters questions. No offense intended...