UE Megaboom has been working great on the boat. waterproof and loud.
Love my booms. Have owned 4, gave two away to folks who were impressed with the sound. JBL are good too. Many of the newer Booms can also float...The booms network so you can get 2 or more and sync them up too I’m about to replace my small boom have had it for like 7 years battery life pretty much shot and the plug connection is a little corroded but still works
Bluetooth amp and wired speakers is 100% the way to go on a new build imoI would skip the Bose stuff and go with one of these, or two of these since they can be paired. Amazing sound great battery and under $70.
Plus it's waterproof. https://www.amazon.com/Cambridge-SoundWorks-WaterProof-Portable-Bluetooth/dp/B07NDPGH55
It's all I use on my boat and it can get as loud as I have ever needed.
Another option that I have in my classic car is a Bluetooth amplifier hooked up to speakers. I used this one and have been very happy with it. Amazon.com: Kenwood 1177524 Compact Automotive/Marine Amplifier Class D Kac-M1824BT, 180W RMS, 400W PMPO, 4 Channel