There is a round, weatherproof electrical box that is a standard in the US, and many electrical product manufacturers supply them. Does anyone makeone of these that has positions for four screws on the 0, 90, 180, and 270 degree positions on the round box? All of the units I have seen have screws in only two positions. If you need to mount the box on the low part of a beam you can leave the bottom part of the box exposed and not flush to any material. It would be nice in such cases to have an additional place you could use a wood screw, to keep the box securely on the place it is mounted.