Hello Stefan, thanks for the welcome!
What type of adhesive do you use, and do you treat the paper with a substance to stiffen it?
For Bridgette, the green battery trammer, the frame is card stock. the battery box actually has a foamcore structure with cosmetic card stock glued onto it. Details are cotton swab stems, staples, card, and thin wire. The buffer beams are card stock and filled with sand for ballast.
For the Dalek, thin cereal box cardboard is primarily used. Printer paper is used for the details, including the hemispheres which were sanded to shape and cut off of tight rolls of printer paper.
For Iseult, the Lister, the frame is made from printer paper folded and glued into a long, hollow tube which is used for stock material for the frame. The engine and details are also printer paper.
Finally, the black motor flat car has a frame made of "slab construction". I took printer paper, and creating an accordion fold structure, and all the layers are glued together. In this way, I can have several layers of paper aligned and glued into a strip of stock material. These are cut to shape and stacked to form the frame and planks on the deck, creating a very solid/strong card frame.
The ties were created from similar slabs as were the rails. The ground was done by layering brown wrapping/postal(?) paper which was crumpled to create the ground texture.
For each of these, I used regular Elmer's school glue (PVA). Only rarely when I use foamcore such as for the trammer or layout bases do I use hot glue. I don't use any stiffener, but I find that if I have enough layers of paper, no stiffener is needed. In fact, if the slab style construction is thick enough, the entire slab begins to behave a bit like wood. For example, it can be sanded to shape.
Finally, in case you wondered, all paint used is acrylic paint.