John Smith wrote:

My goal is to have access to portable power on the water with my kayak
without the risk of electrocuting myself or anyone else!

I'd like to be able to relax and use my power supply without being anxious
or uptight with concern over electrocution.

Is this approach safe?

No problem, 12V is not an electrocution hazard. AGM cells have a very
low internal resistance and probably the most dangerous thing you could
do would be to drop a wrench across the terminals. A fuse right at the
battery would be good. Full immersion wouldn't be a disaster.

-rick-