Body work

I’ve been told the aluminium will be rotten behind the bubbles paint , am I best poking it through and then filling it?

The bubbles are caused by the aluminium oxidising and forming a white powdery residue.
You can clean it of, sandpaper the alluminium and paint with an etch primer, I doubt it will be rotten, it looks like it was just painted badly.
If it is rotten then it will be a differing metal reacting with the aluminium and it may need more attention.

miktdish said:

The bubbles are caused by the aluminium oxidising and forming a white powdery residue.
You can clean it of, sandpaper the alluminium and paint with an etch primer, I doubt it will be rotten, it looks like it was just painted badly.
If it is rotten then it will be a differing metal reacting with the aluminium and it may need more attention.

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I can confirm the truck has been badly painted with its old blue colour coming through in places but the paint on the picture hasn’t peeled yet might have to investigate further

Similar tot he above it will not be rotten but it is oxidation similar to rust. If you compare it to rust the white powder is the orange rust scale. You need it to have gotten pretty bad, similar to rust, before it is all the way through and is "rotten". As said above, sand it back to shiny metal, etch prime it and then repaint with the top coat of your choice.