Advice on custom underwater light

So I'm planning on building an underwater light with convoys 3x21c mcpcbs with 7 x LHP531's and having as many as possible inside my chosen car spotlight host.

The question being how much heat will the convoy 3v 25a buck + 54a FET driver create? I was thinking of a tiny fan stacked on top of 2x drivers so driver^ driver^fan in a stack and considering it will be underwater with a massive finned heatsink it should be ok? Obviously the FET boost won't be used often.

Cheers