I have a circa 1950, Smith Miller Mobil Tanker" truck

https://www.etsy.com/listing/603919326/1950s-mobil-gas-truck-tanker

I used a paint-stripper to remove the original paint.
I sanded the wooden body to a smooth surface.
I applied an undercoat.
I applied several coats of Rust-Oleum "Painter’s Touch" "Ultra Cover" Multi-Purpose Brush-On Premium Latex paint.
I applied the decals.

The decals are chipping off and there looks like air bubbles under the decals.

What did I do wrong?

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