My new Ram has HotSpot and it basically uses my Phone Data plan so really not a good option for me.

I also notice that even in my truck it will drop out Serius pretty easily in the hills out by my house.

On a boat if you don't have cell signal a Hot Spot isn't going to help, your only option is try Serius radio, you can buy a receiver unit and connect it to the boat. Then you are using Satalite radio, more reliable in most settings.

I feel the same as you do about music, I downloaded a lot the first couple summers, now my local lake has a cell tower on the mountain with my carrier, so it helps a ton. I still switched over and got Beats Music on me and the Mrs phones and I can download the tracks to my phone with playlists for lakes we goto with no signal.