Capn,

Don't mean to give the impression of being a 'know-it-all', I only have two books on spitfires:

Spitfire in action - This is just a 60 page 'booklet' This is just one in a series of book that covers many aircraft. I got mine at the Smithsonian in DC. but I've seen them in hobby shops.

Spitfire flying Legend - This is a Barnes & Noble book, lots of nice pictures. They were selling it off at half price so you might not be able to get it now...

All of the info I've typed here has been from these two books.

As for the wing design, I have no notes about the design of the Spitfire; the books deal mainly with the specification of the different variants. I doubt that it had anything to do with the amount of internal accommodation it gave, probably more to do with aerodynamics. Mitchell based the design on his high performance racing seaplanes.