My suggestion would be to jettison SWIG. Of course I dont have any experience with SWIG but I do have experience with Inline::C so this isn't coming from an unbiased viewpoint. :-)

Anyway, Inline::C will automatically wrap most C functions with the appropriate XS glue. Occasionally it needs help with special typemaps but not often. Besides that constructing an SV with the appropriate properties is quite easy, but you will need to know the length of the buffer and the utilized part of the buffer for it to work. IMO you should immediately go an download Inline::C and play with it. It is not difficult to use at all, and probably will help you design a Perl/C interface layer for your code much easier than SWIG will.