Oh, the best OB bracket for the money is the Garhauer OB-125.
I think I paid $180 for it and the quality is far superior to any of the others I looked at, but at about half the price. I do not know if you will be able to get it in the UK easily, though
Also, be wary of keeping a gas tank in your locker. We keep ours outside to prevent fumes leaking down into the bilge or cabin.