HI Denzel
I have one of the original Airfix models. I did not build it and on first sail it leaked badly. The culprit was the rudder shaft or rather the lack of any. I fitted a new shaft and sleeve and made sure the shaft extended above the waterline. There is room but it is tight. I also replaced the shaft bearings which were worn. Tne inside is very similar to your model but the servo is near the stern and I use a 6v 4Ahr SLA placed in the middle of the hull. The whole of the top to the front lifts off so access is good. I use an old Hitek esc and 2.4 rc. Sails well but is not really a rough weather model.
Dave

Hi, here is a 6mm hole in the keel which I will be plugging hopefully I can do her justice and make a nice model out of it.

Judging by the included pump he expected to take on water! Has any of the body been chopped out?

http://www.strikemodels.com/

Have a look there. I may be wrong but I can think of no other reason to fit a pump from the get go unless a model has a fire monitor.