I'm creating a layout for a skirmish scenario and I want to make the scenery permanent. In other words, I'm not going to pull these walls, etc. down and use them for something else. What I need is a good way to mount ClipIt walls on the tiles so they stay put. Since there are no horizontal pieces to the walls I'm not sure how to approach it. The floor tiles are going to mounted on cardboard lids from copier paper boxes.

Any ideas are appreciated.

Which set are these walls from?  You might try useing strips of floor tile and making little "wings" for the bottom of the wall, sort of like how the Caveworks floating walls have.  
Just take an inch or half-inch wide strip of your floor tile, give it a score lengthwise down it's center, fold it 90 degrees, and glue it to the inside of one of the wall sections before you fold and glue the wall section.  Use one on either side for extra stabilty, and there you go!  If you glue it down, it should stand up straight and be as permanent as you want it to be.

The walls are from CK & GR, but the tile is GR. That sounds like a good idea, Carjack. I'll give that a try!  :)

Try folding the wings under the wall section to hide them, if necessary.  I assume he was suggesting you glue the tabs inside the wall sections?  A card-stock "L" piece will do the trick nicely.  If you fold them under the wall sections, you can use your cut-offs:  "recycle, re-use, reduce."  Cheers!

This is the one area where Dungeon Works Classic wprks better than Gothic Realms. I prefer permanent structures myself, I use them at conventions etc. and then give them away as prizes, The first set I ever built was DW, which we mounted as seperate rooms to foamcore. For GR... I have only one  idea. (I printed up way too much DW and am only now starting to get near the bottom of the pile...)

Maybe you could make some right - triangular tubes from  some extra corridor and room sections, cutting them to match the bottom 1/2 inch or so of the corridor along the angled bit and gluing the right angled parts to the corridor and the masterboard. The downside of this is that you will end up printing around twice as much tuff. (Unless you're good with Photo Shop, in which case I envy you. )

Helping put together a friend's DW prompted me to look over the WW stuff on the GMs Day a couple of years ago. I ended up buying C&K first, but used DW more quickly.

The Auld Grump