[Papercaptain]

Good afternoon, doctormax!

Well, there's always the wall to fix it on. When I was a boy, my ship models were put on shelves made of thin plywood (around 3-4 mm, with stiffening frames around the edges). These were connected in 3 tiers by pieces of string and then hung from a peg at the wall. Like this: /\
.................................................. ......./__\
.................................................. ......[___]
.................................................. ......[___]
If you are not so delicate about materials you could do this in a similar fashion but using thick triple glued cardboard or corrugated cardboard (Wellpappe) instead.
The other way would be making a shelf of thick (triple) cardboard the size of the ship, adding two triangles at both ends and bending them down at points a and b like this:
_ a_________________________________________b__
\ |................................................. ..................| /
.\|__________________________________________|/

Now you can glue some straps of bristol cardboard (reinforced with aluminium cut in form from yoghurt lids or something) to these points reaching slightly over the surface of the shelf and then nailing them unto the wall.

Kind regards -
Papercaptain