The two Ikelite lights might be the easieist to mount on the Ikelite case, but you need to consider what you plan on photographing. In today's light technology, the Halogen based Ikelite Pro Video is an inefficient way to produce light. This means a shorter burntime underwater or a pretty heavy battery pack. State of the art lights are LED based. These are long life and much more efficient at converting electricity to light.
As to the Ikelite Pro-V8 LED, this is only 250lumens. As an example the Light & Motion Marcro250 is also 250 lumens and it is application-positioned for MACROS i.e. close to your subject. For more typical distances the Light and Motion Sunray 1000 and 2000 provide 1000 and 2000 lumens respectively.
My point is-- unless you are going primarily for MACRO I recommend that you should have more light output AND for best burntime with reasonalbe battery packs, I'd opt for LED based videolights.
Check out the other lights folks have suggested!
ArtF