For 5 years I have been looking at the ends of the terracotta chimney flue liners I used for tunnels. I couldn't decide on what to use for a tunnel portal. This past spring I bought a good Rigid table saw and a portable compressor that came with three nail guns. The 18gauge gun seemed perfect for building 1/29 structures. I also got a 23gauge pin nailer for really small stuff. 

Well, having the right tools makes all the difference in the world. I cut down some scrap PT 4x4 I found on someone's curb and built these tunnel ports. I had seen a picture of a wooden portal with the braces as shown. I liked the affect and incorporated into my design. I made these up as I went, cutting and nailing. I could not have done it with out the right tools. Finally, after 5 years I have tunnel portals hiding the flue liners.