Huh! I’d print some nylon straps, or strap it in somehow. That’s got to be a lot of weight. No doubt the fiberglass can hold it though… so maybe it will be 100% all good. That thought just gives me the slight uneasy-s
If you glue them with neutral silicone to the board you will be completely fine
Just cover the whole place where the battery will sit with a generous layer, clean the battery really well, put weight on it and let it dry
I’m still tying to figure out how I will remove my old battery without destroying it in the process
just a suggestion for the attachment of the enclosure, drill through the deck and use “t nuts” on the foot side of the deck. find out the length of screw you need and use em. then put griptape over the top. it’ll be far stronger than inserts