Hull structure
That looks like jacking damage but it's very difficult to tell from that picture. It appears that it is far enough back that you should be able to examine the interior of that area in the rear bilge - it might require removal of the battery / water tank support base if it's too far outboard. I would recommend getting a good look at it from the inside if possible. Whatever it is, it should be quite repairable.With regards to the water in the bilge...you say that it's on the trailer but not coming frmo rain? What are the other possibilities? I did extensive work on my Hunter to eliminate the leaks and was succesfull with the exception of the rear locker access seat where the lip in the channel that should guide water away is not tall enough just under the seat - I'll form a taller one soon. However, the biggest leak that I had in the boat was the hull to deck seam under the rub rail. If the boat was sitting flat and tilted forward it would be no problem but because the rub rail fits tighter to the hull on the flat stern, water would run into the rubrail along the sides, flow inside the rail to the stern where it couldn't escape. The sealant at the hull to deck seam was cracked and water would come in at a very high rate - almost pressurized! If your cover is not keeping water off the rub rail around the entire boat you are probably leaking there too.Jake