Question on TV mounting for 21NE

[Endymion42]

Hi,
New owner of a 21NE. I ordered the 1/2" reinforced wall between the bathroom and the dinette area and plan to mount a TV on the dinette wall approximately where the medicine cabinet is on the other side of the wall. Has anyone taken off the medicine cabinet and see if the back of the medicine cabinet abuts directly to the wall or is there any type of air gap? Or more to the point, what is the longest screw I can put in the dinette wall without penetrating the medicine cabinet?

Thanks for your thoughts,
John