This is a great start and a fantastic job on the cockpit. Those two bottles are actually compressed air, usually found silver coloured, but also grey.
It is interesting what you have done with the brownings, I was planning something similar before asking for some help from the lads over at Britmodeller. The guns were actually butted up against blast tubes so the muzzles/barrels would not be seen at all. The blast tube was set flush within the wing leading edge, but there is some instances of them being set in slightly inwards.
quote from Edgar,
This is one of those "Jury's still out" questions, since there are a lot of "maybes" involved. It appears that the early Mk.Is had tubes, with a slight "step" inside, which might have been for the "covers," mentioned in the September 1940 modification (which introduced the fabric patches) to rest on. So far, I've been totally unable to find out what the covers (there were others in the empty case chutes, as well) looked like. It's always been a bit of a mystery why Supermarine decided that the introduction of self-adhesive fabric patches needed a full-blown modification, but, if it meant changing the design of the tubes, it makes more sense.
The steps appear in a drawing of the Mark I leading edge "D" box, but with no indication of their purpose, and disappear in later Marks. There is no sign of any form of external cover in photographs of early airframes, and it's difficult to believe that freezing-up wouldn't have been a problem, since the Brownings were cocked before take-off, so cold air would have gone straight into the breeches.
Certainly they had icing troubles with the early cannons, and found that rubber sleeves (cue condom jokes) were less than ideal, because the cold made them go brittle, then shatter, with bits entering the barrels.
The tubes were definitely not free-floating, but fixed at each end.
regards,
Jack