mine's just to the port side of center (the left side if you're facing the bow of the boat), and all the way aft (toward the back of the boat) against the transom
mine's also not permanently mounted so i can move it a little bit in order to clean out leaves, grass, sand, mud, etc... that inevitably collects in the bilge area
my bilge pump hose is heater hose which is much stiffer than bilge hose, & the hose is secured everywhere except the last 1' or so of hose by the pump itself which allows me to flex the hose around to move the pump a little bit but still keeps the pump in place while underway, even in rough water. i have it installed so that it's wedged up against the knee bracket by the hose, that way it stays pretty much in place but can be moved very easily. many folks permanently mount their bilge pumps, but i never have because i like it to be able to be moved around for cleaning and also so i can put it in the deepest part of the pool if i have a lot of water in the boat
in a small boat, it's not that critical, because you can easily move around weight in the boat to make the water pool on one side or the other for the pump to remove it, but on a big boat, you have to put it in the lowest spot for obvious reasons
if your going to secure the pump itself, i suggest putting it in a rear corner on a small boat, because it's easy to get the water back to the rear corners, but if the middle works better for your looks or something, that's fine too as long as it's near the back. the bilge pump cannot pump out the last 1/2" or so of water anyways, so wherever you mount it in the back portion of the boat should be fine
