Let the build begin. Coach bus.

[kaptain Jack]

Thanks for the link, Frizzen, the reason I chose for the subfloor: is to add rigidity to the tall structure and to have extra space for compartment. Bulkheads are just scraps of material, since,once complete, become invisible,but carry the functionality.
I used 3mm (1/8'') styrene for the same reasons of durability and rigidity, also the thickness helps to round the corners for more aesthetic look. And speaking of rounding the corners. When using the file,common mistake is to move the file in the shape of the curve, its logical,but wrong! exactly the opposite is what will give you a right curve. When working the corner, the file must resemble a bottom of rocking chair,swinging in an opposite circle motion. As a young man I worked as a goldsmith and first thing they teach you,is how to make ring by filing down a square profile.