Discussion
It looks to me that whatever was put on to protect them is loose, or coming away. You need to scrape off everything loose including any powder coating that is flaking off to get to the metal underneath to check. They usually go in the corners first which you can just about test with a screwdriver, or check with a borescope, but the only way to be really sure is to lift the body.
If there's no actual holes, some treatment and protective coat will keep replacement at bay a while, depending on whether you use it all year round or not. 
The condition of the tubes that you actually can see are an indicator though. I've seen cars (Chimaera and Griffs) with visible holes in the tubes at the outrigger corners that had not even been mentioned on MoT examinations.


The condition of the tubes that you actually can see are an indicator though. I've seen cars (Chimaera and Griffs) with visible holes in the tubes at the outrigger corners that had not even been mentioned on MoT examinations.

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