Makeshift "Airtight" 2x2 With Some Glue, What Do You Think?

Guybrush:
I note that you are in Indonesia.
Very humid climate, I understand the need for airtight 2x2's.

Unfortunately, the very thin Mylar film used in 2x2's is very slightly porous, and can become sticky, when used with PVC album pages.
That is certainly MY experience, and I live in Sydney, where we can also suffer very humid days, but much less often.

It is much better to change to archival quality polypropylene or Mylar album pages. They don't cost much more, but can be harder to get. In the case of Mylar album pages, the film is MUCH thicker than what is used in 2x2's

All is not lost, however. A similar approach to what you have suggested CAN be used.
Hard acrylic sheet, like Mylar, is harmless to coins. This is the plastic used for slabs.
Acrylic sheet can be recovered from food packaging.
Cut 2x2 squares from this material, and use these INSIDE your 2x2 cardboard / Mylar flips.
Proceed as you have suggested.

Experiment with which glue may be most suitable for this slightly different approach.

I don't use glue, I just staple the whole lot together, BUT what I do is not airtight.

I agree that a whole album of coins could be stored in a polyethylene clip lock bag of suitable size. Some CCF members do this in the more humid southern areas of the United States.
Also useful for the storage of a banknote collection.

As pictured, you have the right sort of food containers.
Hard clear plastic sheet.
Has to be carefully cleaned, to be free from food contaminants.

Polyethylene as is used for clip lock bags OK for coins, but unfortunately, is only translucent and not a suitable material for seeing through.
Small polyethylene bags with a single 2x2 inside, are not suitable looking at the coin.
As mentioned, polyethylene clip lock bags can be obtained, that are large enough to put a whole coin album in, away from humid air.

Cyanacrylate UHU glue should stick to acrylic, but be beware, it is liquid, it depends on moisture for setting, and can stick your fingers together! DON'T GET ANYWHERE NEAR YOUR EYES!
Also hard to control, because it is runny until set. It will set faster in a humid atmosphere.
DEFINITELY have some acetone solvent close by! USE this glue VERY sparingly, and perhaps with a thin circular gasket of of acrylic plastic. You will need to develop skill when handling UHU glue in this sort of situation, could get messy otherwise.

My brand of cyanacrylate glue just happens to be UHU; some confusion in glue types here.

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NOTE:
You may wish to consider spruett001's suggestion of heat sealing. It may end being a more practicable way to go.

Just put the coin in a smaller pair of squares of Mylar of appropriate size, heat seal with a knife, and dab glue the square at the corners into a 2x2.

They do make self-adhesive 2x2 holders, which would accomplish the same thing with less hassle.

The self adhesive 2x2's use the same thin Mylar as the stapled type.

As mentioned earlier my experience is that the Mylar can become sticky when they are in PVC album pages. The Mylar can be torn when you try to remove from the album page.
Hardly a solution to trying to achieve airtight! Atmospheric humidity does NOT help in this situation.
That is one of the reasons why I replaced all of my PVC album pages with NON PVC.

Use too much glue, and it would spread out, onto the coin. There are so many other, better solutions.

You ever try painting without getting any on you then accidentally touching something? Same goes with glue! I've had coins stapled into regular 2X2's since I was a little kid with no problems.

Good choice.