A further report on method 3 from my previous posting......

Not sure if this has been done before but it is only a twist on the plywood and rivet method. At the baseboard edge, holes have been drilled through the plywood sleepers, and through the balsa underlay into the plywood track base. Then 20mm long panel pins have then been pushed and lightly tapped into place.

The rest of the blog, with pictures, can be found here