any tips for removing rust inside the cowl ?

[Iceman_70]

When looking inside the cowl, I see there is 'some' rust ...



Luckily, the inner and outer cowl is still pretty solid … I just had to replace the lower hinge pockets…
I have some anti-rust products, but does anyone have some tips on how to access this area and remove/convert the rust ?
Options that passed my mind :
- Cut a piece out of the upper outer cowl -> when welding it shut, you keep an 'unprotected' weld on the inside
- Remove the upper outer cowl by drilling out the spot welds -> don't even know if this is doable ...