Hey Swang! That is a cool looking model!

One thing that I usually try, is copying the surface and scaling it (normal or even 2D scale in two steps) to get the two surfaces in a convenient position. Then run a naked edges command, Join the selected naked edges and you should have 2 closed curves with similar points. Then you loft the two curves and you join the resulted surface with the initial and scaled copy. Usually I have a solid after this. Not guaranteed, but worth the try since it is pretty quick!