That much for underwater LEDs? Good grief, I'm in the wrong 'bid-nez'! Except for the wires coming out of the back of the LED, they're water proof to start with. Water proof the wiring and make a housing, you're done.
For an R/C boat, drill the right sized hole, insert LED so that the end sticks out of the hull, glue seal the hole, you're done.
They really get that much for an underwater light?
- 'Doc