@Pingles, please be a little more gentle in the ways you say things. I want, I need, I... And although you want a tunnel and I can understand that (my dad made me a paper-mache one when I was 8 or so, good old 12V days ;)) and I also like tunnels, you better try to make one in LEGO Digital Designer or so. This isn't the place to discuss non-LEGO tunnels I guess...
Sites like http://www.floodland.nl/aim/ that are targeted to model railroads have nice ideas on how to use the materials you want to use.
@LEGO Man Can: they are just too expensive. You could buy a lot of LURP / BURP bricks from LEGO @ home.