Sir,

Generally the sliding plate support is designed in such a way that even at the utmost displacement in all directions the sliding plate is not exposed . The upper and lower plates are made out of SS,and the dimensions are selected after checking the displacements.
Also i doubt whether painting will be done underneath the pipe shoe

The third condition, I have no answer , in that case also i doubt bird building a nest at almost grade elevation.

Please forgive me if i am wrong and thank you for clarifying