Using oil based paint to protect your plywood was not/is not, a bad idea, nor the cause of your troubles.
You didn't say if the bubbles are in the paint, or in the plywood, but either way, moisture is causing the bubbles.
It could be getting in through the edges of the plywood, a window or door cutout that didn't get any/enough sealer/paint, or it could be migrating from the other side of the plywood.
It could also be a case of two coats of paint not being enough to completely seal the surface.
I have no idea how you painted the wood, and mean no offense, but most people do a fantastic job at painting/sealing/varnishing that which is visible, but pay very little, or no attention the cutouts, edges, and the reverse side of a given project.
The type of wood, and which side makes a difference too.
Some species of wood can be properly sealed with two coats of oil based paint, some can't.
Plywood for example, can sometimes be sealed well on the face with 2-4 coats, but the edges, or endgrain may take 8 to attain the came level of moisture protection.
Can you provide more information, and or pictures of the bad areas?
Waiting for "someday" will leave you on your deathbed wondering why you didn't just rearrange your priorities and enjoy the time you had, instead of waiting for a "better" time to come along...
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