Hello,
you made some very nice models of Japanese ferries!
I myself also do modelling in paper and cardboard, in small scales like 1/500.
For instance containers I design in Excell spreadsheet software and print it to scale, that works very well.
For some details like winches on the bow or stern I use pictures copied into Word software and printed to scale and then cut out and glued on place. It is still not 3-D but better then nothing.
For lifeboats I use small woods, sanding it at stern at bow, cutting it into shape.
Can you show use some more models made by you?
Regards, Pieter