i think you're not seeing the walls properly because of the shading. they do have actual thickness. you can see it on the ports at the left of the picture. i do think though that the planking looks a bit odd on the inside of the wall. it's realistically done on the outide, but the inside is a bit unrealistic. you've created the illusion of a bit more structure on the outside than you've done for the inside, in the sense of vertical beams.
Yep, thats not finished now, will be worked next.