Gale has never proposed anything at camp because I think I haven't had him go through the death scenario. My druid was too good at keeping him alive. That, or something else overrode the scene needed and I have no clue what.
Gale has, by far, the most dependant flags in order to get him to propose intimacy; for all of the others, you'll get their offer as long as their affinity is high enough, without any particular scene being dependant whereas, with Gale, every single one of his side scenes, up to the weave scene, are necessary to progress and some of them are missable because they only fire at certain affinity levels, and it's incredibly easy to shoot past two affinity levels in a single rest cycle or singular chain of events and choices, which can lock you out of romance regardless of having exceptional, capped-out affinity with him.
In order to ensure you get all of Gale's flags, you can follow these steps:
1) Go pick Gale up right away once you're off the ship (not strictly necessary, but don't, for example, go to the ruins, or the grove gate, before collecting him)
2) Take along rest just before you pick him up, to clear other companions events, then take along rest immediately after collecting him.
3) Keep Gale in your party at all times, so that he's with you for every choice you make - as much as Larian perpetuates the "everyone knows everything you did or said regardless of where they are" mess that they've carried over from their previous game (and just put a silly lampshade on with the tadpole even though it's clearly not a two-way street), some events seem to still need the character with you actively for them to register their acknowledgement of your actions there.
4) Take a long rest every single time you make any kind of decision that *anyone* approves or disapproves of, even if it wasn't Gale.
5) Take a long rest any time you make a decision about a situation or how to approach it, even if *none* of your companions approve or disapprove.
6) Take a long rest every time you enter a new area as well.
7) Yes, even though this means you'll take a half dozen long rests while in the druid grove, between most conversations.
8) Yes, this means you'll be taking a lot long rests even while his actual visible affinity doesn't change - you'll take *many* rests to trigger events while on neutral and on medium.
9) If you get the Weave scene at any point (and you might have to save scum in order to succeed the four or five checks that you need to make to progress it... otherwise, again, you're locked out), and imply intimate interest to Gale there, then you're set. Otherwise, continue to do as many of your pre-underdark objectives, areas and events as possible before hitting the goblin camp, until you've triggered it.
This may seem a bit overkill, and it probably is, but being this pedantic about it is the most reliable way to ensure that you get it.