My loadout for squid hull is Spanner, Wrench, Chem. Any time I throw any kind of a cooldown on a squid hull, it spells immediate armor death. Heck, I never even put out fires with the chem spray, only use it to pre-spray outside of combat.
I've seen some maths that strongly suggest using the wrench is better for rebuild as long as you're not overhealing, but in practice I've had little luck. I'll maybe get a small handful of opportunities where I feel the wrench is the appropriate option. I usually just spam spanner the entire time, and it works quite well. 4 clicks to rebuild armor means you're pretty much safe outside of a literal 1/2 second of armor down ... as long as you're already ready and clicking with the spanner right before the hull armor goes down.