Narkissos....It's true that, outside of Genesis 6-7 (where only in the redaction is J's "rain" associated with P's "watery deep/windows of heaven") it is only in extrabiblical sources that the heavenly waters are directly connected with "rain" and "clouds", e.g. 3 Baruch 10:6 which construes the heavenly lake waters as "that which the clouds receive to send as rain upon the earth". But the way P associates the verb ptch "open" with 'rbwt "window" in Genesis 7:11, 8:2 is still parallel to 2 Kings 7:2, 19 and Malachi 3:10 where the two words are used to refer to ordinary rain, presumably delivered by clouds. And the two are also used in the Ugaritic Baal Cycle to refer to Baal "opening a rift in the clouds" (KTU 1.4 vii 25-39) to bring rain on the earth, so the connection between "opening the windows of heaven" and clouds was something inherited from Canaanite cosmology. I agree that there is not one single cosmological system in OT texts.
The Society's discussion of the matter in the Insight book involves much special pleading. If material from Job, Genesis, or other OT books diverges from modern cosmology or scientific knowledge, the Society claims that the references are "figurative". But if they somehow can be construed as coinciding with modern knowledge, all of a sudden the statements in the very same books are no longer figurative but "scientifically accurate". If the statements are to be dismissed as mere poetic turns of phrase, one should also recall that the Baal Cycle, the Enuma Elish, etc. are poetic compositions as well, and thus all the mythological elements in them could be dismissed as figurative poetic metaphors....and thus we could also credit the ancient Canaanites or Babylonians with modern scientific knowledge in those rare instances when they describe things that could be construed in some strained way as reflecting scientific accuracy.
So the statement in Job 37:18 is taken to be a mere poetic metaphor:
That the literal beating out of some solid celestial vault is not meant can be seen from the fact that the word "skies" here comes from a word (sha´chaq) also rendered "film of dust" or "clouds" (Isa 40:15; Ps 18:11), and in view of the nebulous quality of that which is ‘beaten out,’ it is clear that the Bible writer is only figuratively comparing the skies to a metal mirror whose burnished face gives off a bright reflection.
The text does use a metaphor (kr'y mwtsq "as a cast-bronze mirror"), but the Society inverts the figurative relation. They claim that the author is comparing the brightness of the sky to a figurative beating out of a metal mirror (which becomes reflective in the process). But the actual simile is that beating out a cast bronze mirror (which becomes reflective in the process) is figurative of God's beating out of the heavens. The Society's explanation thus embeds a simile within another metaphor (a rather unnatural reading), and it turns on shchq "skies" indicating the brightness of the sky (like a "mirror"), but the root has the sense of "rub away, beat fine, pulverize" (cf. Exodus 30:36, 2 Samuel 22:43, Job 14:19, Psalm 18:42), which naturally relates to trqy` "beat out" -- the very meaning they want to dismiss as figurative.
And while this whole passage is viewed as figurative, the similar nature poetry of the preceding chapter (ch. 36) is suddenly regarded as non-figurative, as a naturalistic scientifically-accurate description of the water cycle (Job 36:27-38). But this "accuracy" is more an artifact of the translation in the NWT ("For he draws up the drops of water; they filter as rain for his mist, so that the clouds trickle, they drip upon mankind abundantly") and some other versions (such as the NIV), than is justified by the original Hebrew. The "scientific accuracy" turns on how the verb gr` in 36:27 is rendered; in the NWT, it is translated "he draws up", which is suggestive of evaporation, but it usually means "draw away" or "diminish" (cf. Exodus 5:8, 19, 21:10, Deuteronomy 12:32, Jeremiah 26:2, Ezekiel 5:11) or "restrain", "withdraw", or "take from" (cf. Job 15:4, 8, 36:7, Ecclesiastes 3:14), so the highly suggestive "draw up" is not entailed by the Hebrew...one could otherwise say "He draws away the drops of water" or "He restrains the drops of water", etc. The Aramaic rendering in 11Q10 (tho fragmentary) and the LXX render the verb as "to count, number", suggesting a different way of understanding the verse (and connecting it to v. 26): "He numbers the clouds of water, and the storms of rain pass by, and his clouds bring down drops of water on many people". Another uncertainty is 'dw in v. 27 (= Genesis 2:3), which probably does not mean "mist" and which may mean "flood" or "cloud" (as it is in 11Q10 and the LXX).