I can't think of anything causing an explosion in a kayak electrical system other than getting saltwater into a battery, or, more likely, a short circuit over-heating a battery that is housed in a sealed box or bag. It wouldn't take much heating to pop a waterproof battery bag or a box. You have to keep water out of the battery container and always have a fuse on the battery cable. Any significant heat source on a plastic boat could be a very bad thing.
I guess I should start installing a CO2 flooding system in the electrical distribution compartment on my kayak
