Good stuff so far Geo. Regarding the fuel filler - many kits have the filler moulded this way, which might be an attempt to replicate the recessed filler on later Spits, which had an armoured cover.
For the rain deflector on the camera hatch, bend a piece of stretched sprue to form a semi-circle, cut to the required dimensions, cement in place, and, if needed, build-up the 'streamlined' part with Milliput. If you haven't removed the hatch totally, as already discussed, punch the clear 'window' from clear sheet, and drill and ream a hole in the fuselage to fit.
EDIT: Just noticed, the hole is already done! Also noticed that the starboard side cannon cover in particular, looks like it might need lifting at one edge, and possibly blending-in a little.