[LBR=Rademacher]

the concrete bunkers are objects ...listed in the static ini
try adjusting the Panzer setting and this will make them harder to destroy.
but guns placed within them will not fire...

the howitzers can also have their maximum range increased in the Technics.ini ...but their shells are not very powerful..... the russian 85mm AA/AT gun is quite accurate against tanks...but at ships and with increased range i don't know

the huge german tracked guns have a long range and can be effective against ships...but their shells are lobbed and not very accurate

What about the two bunkers that came with the last regular game update? They have firing guns, could they be transformed or their files be used to create for danger is looking for?

I think they're regular artillery objects built to visually look like a bunker. That can be done again, i believe.