This one has been in my "To Do" pile for weeks so it's time to get it built before my furry Doomsday Machine gets to grip with it. I started with a Drex File from Ex Astris Scientia, shrunk it to 50% and pasted a few copies on my sheet so that 2.5 could be fitted across an A4 page. I also stretched some sections in MS Paint where curves were involved. I printed a page on 200gsm and another on copy paper (just in case). This is the starting orthographic:-
I chose the plane with the most surface area to act as a base; the red line below shows the plane I chose:-
This gave me an upper and lower face to start building on:-
This needed to be bulked up so I added a strip incorporating the curves to the top and two central strips to the bottom:-
Next, I concentrated on the undersides of the 'sleds', the protrusions under the hull and a mount for the weird-shaped thing at the back. None of the views in the ortho's showed the mount so I used some artistic licence:-
That done I cut pieces for the sides and top of the 'sleds':-
The sides were sections taken from the elevation and stretched to increase their height. The elevation was flipped to obtain the starboard pieces. Once these were glued I moved onto the upper hull, sled mounts and the ventral fin at the front:-
This left me with the aforementioned weird bit - the reason I've been putting this one off for so long. In the end it went together surprisingly easily:-
Et viola! A 1 3/4" (45mm) long Karemma merchant ship waiting to be mounted 
I'll probably write a more in-depth set of instructions in my blog. This is a bit rushed as it's after 3am and I can hardly keep my eyes open... 
good luck!.