That fixture should be OK with the legs on it. One of the factors that you have to look at is; what is the surface doing? If you have any air breaking the surface water, you will end up with water on the fixture. I dont recall this fixture completely, does it have any cover over the fixture or the bulb mounts? The end caps for the bulbs are the most important thing to keep dry.
It has an acryllic cover that slides into the fixture to cover the bulbs. There are small ripples that go across the surface from the return on my canister filter and the mj600 powerhead.
The ripples are no problem. Its air that creates the problem. If you have the air hose attached to the powerhead, take it off. Make sure the outlet of the filter is at or below the surface and you will be fine.