Just to clarify, Gel and AGM batteries are often confused.
One key to a clean and seviceable amplifier panel is to have plenty of extra real estate for distribution, wire raceways and strain reliefs/tie-downs.
The hull surface of that year probably will not give you direct mounting provisions, but once you resolve that you will have a very spacious panel for multiple amplifiers, possibly a battery charger, and all the necessities. The ability to service and tune will be a breeze.
There really are not many good alternatives for mounting batteries beyond the sole of the observer's locker. You can usually move the batteries forward to give more storage room. Just make sure that the battery switch is positioned just inside the locker opening for convenience. Every wire/cable feed can be easily extended. But you may want to look over the length and access of the heavy B+ and ground coming from the engine in advance before planning a relocation.

David