Ben: My recommendation would be to use four DC-grounded folded vertical dipoles spaced around the perimeter of the water tank, and fed with the appropriate phasing harness. Check out Cushcraft's comm
As Ben indicated, multiple antennas with any significant spacing will generate a multi-lobed pattern with lots of nulls. This will be the case with or without reflections from the water tank. Even th
Yes, I sort of figured that the 'around the catwalk' idea was a problem and didn't consider it too much because I figured you'd need a lot of antennas to get good coverage without significant nulls.