I guess we all run into this issue. This was my solution. The bracket is aluminum that was clear coated with a thick spray used to coat tool handles.
The bracket was bent to allow a clear path for debris and water to flow out of the drain plug, also for cleaning the bilge.
Bending it 45 degrees instead of 90 makes it less likely to crack and no heat is needed. The Screws and washers are stainless.
You'll notice its a little off center too. (maybe like me
)
Its been in 4 years now and stills looks like it did when first mounted in this photo.
I designed it to bolt it higher on the transom for easier reach for both installation and i f I need to remove it. It is sealed with 3M5200.
Screwing into the transom isn't a worry as there is a 2" thick wood core to hold it but there is a worry about introducing an entry point for water to get to the wood, hence the use of 3M5200 to seal it. 3M5200 Is the WD40 / duct tape of the boating world.
I used the pump I had after cleaning it up but may upgrade it to a better pump or mount a second higher volume pump as a backup.
***One last important note, you'll notice how I've routed the pumps wiring straight up. all connections are covered with shrink tube that has marine sealant.
DO NOT ALLOW YOUR WIRES TO LAY IN THE BILGE. They are waterproof but only to a point. Constantly soaking the jacketing in that small amount of water that lays in the bilge will eventually do its damage. A pump is safety equipment, don't take it for granted and don't take short cuts.